Engage directly without intersecting. . No skill, if i-> j is chosen, then (i, j) is chosen.
// powered by c++11
// by Isaunoya
#include <bits/stdc++.h>
#define rep(i, x, y) for (register int i = (x); i <= (y); ++i)
#define Rep(i, x, y) for (register int i = (x); i >= (y); --i)
using namespace std;
using db = double;
using ll = long long;
using uint = unsigned int;
using ull = unsigned long long;
#define pii pair<int, int>
#define fir first
#define sec second
template <class T>
void cmax(T& x, const T& y) {
if (x < y) x = y;
}
template <class T>
void cmin(T& x, const T& y) {
if (x > y) x = y;
}
#define all(v) v.begin(), v.end()
#define sz(v) ((int)v.size())
#define pb emplace_back
template <class T>
void sort(vector<T>& v) {
sort(all(v));
}
template <class T>
void reverse(vector<T>& v) {
reverse(all(v));
}
template <class T>
void unique(vector<T>& v) {
sort(all(v)), v.erase(unique(all(v)), v.end());
}
void reverse(string& s) { reverse(s.begin(), s.end()); }
const int io_size = 1 << 23 | 233;
const int io_limit = 1 << 22;
struct io_in {
char ch;
#ifndef __WIN64
char getchar() {
static char buf[io_size], *p1 = buf, *p2 = buf;
return (p1 == p2) && (p2 = (p1 = buf) + fread(buf, 1, io_size, stdin), p1 == p2) ? EOF : *p1++;
}
#endif
io_in& operator>>(char& c) {
for (c = getchar(); isspace(c); c = getchar())
;
return *this;
}
io_in& operator>>(string& s) {
for (s.clear(); isspace(ch = getchar());)
;
if (!~ch) return *this;
for (s = ch; !isspace(ch = getchar()) && ~ch; s += ch)
;
return *this;
}
io_in& operator>>(char* str) {
char* cur = str;
while (*cur) *cur++ = 0;
for (cur = str; isspace(ch = getchar());)
;
if (!~ch) return *this;
for (*cur = ch; !isspace(ch = getchar()) && ~ch; *++cur = ch)
;
return *++cur = 0, *this;
}
template <class T>
void read(T& x) {
bool f = 0;
while ((ch = getchar()) < 48 && ~ch) f ^= (ch == 45);
x = ~ch ? (ch ^ 48) : 0;
while ((ch = getchar()) > 47) x = x * 10 + (ch ^ 48);
x = f ? -x : x;
}
io_in& operator>>(int& x) { return read(x), *this; }
io_in& operator>>(ll& x) { return read(x), *this; }
io_in& operator>>(uint& x) { return read(x), *this; }
io_in& operator>>(ull& x) { return read(x), *this; }
io_in& operator>>(db& x) {
read(x);
bool f = x < 0;
x = f ? -x : x;
if (ch ^ '.') return *this;
double d = 0.1;
while ((ch = getchar()) > 47) x += d * (ch ^ 48), d *= .1;
return x = f ? -x : x, *this;
}
} in;
struct io_out {
char buf[io_size], *s = buf;
int pw[233], st[233];
io_out() {
set(7);
rep(i, pw[0] = 1, 9) pw[i] = pw[i - 1] * 10;
}
~io_out() { flush(); }
void io_chk() {
if (s - buf > io_limit) flush();
}
void flush() { fwrite(buf, 1, s - buf, stdout), fflush(stdout), s = buf; }
io_out& operator<<(char c) { return *s++ = c, *this; }
io_out& operator<<(string str) {
for (char c : str) *s++ = c;
return io_chk(), *this;
}
io_out& operator<<(char* str) {
char* cur = str;
while (*cur) *s++ = *cur++;
return io_chk(), *this;
}
template <class T>
void write(T x) {
if (x < 0) *s++ = '-', x = -x;
do {
st[++st[0]] = x % 10, x /= 10;
} while (x);
while (st[0]) *s++ = st[st[0]--] ^ 48;
}
io_out& operator<<(int x) { return write(x), io_chk(), *this; }
io_out& operator<<(ll x) { return write(x), io_chk(), *this; }
io_out& operator<<(uint x) { return write(x), io_chk(), *this; }
io_out& operator<<(ull x) { return write(x), io_chk(), *this; }
int len, lft, rig;
void set(int _length) { len = _length; }
io_out& operator<<(db x) {
bool f = x < 0;
x = f ? -x : x, lft = x, rig = 1. * (x - lft) * pw[len];
return write(f ? -lft : lft), *s++ = '.', write(rig), io_chk(), *this;
}
} out;
int n, m, s, t;
const int maxn = 3e4 + 43;
const int inf = 1e9;
namespace Dinic {
int head[maxn << 6], cur[maxn << 6];
struct List {
int v, nxt, w;
} e[maxn << 7];
int cnt = 1;
void add(int u, int v, int w) {
e[++cnt] = { v, head[u], w }, head[u] = cnt;
e[++cnt] = { u, head[v], 0 }, head[v] = cnt;
}
int d[maxn << 6];
bool bfs(int s) {
memset(d, 0, sizeof(d));
queue<int> q;
d[s] = 1, q.push(s);
while (!q.empty()) {
int u = q.front();
q.pop();
for (int i = head[u]; i; i = e[i].nxt) {
int& v = e[i].v;
if (!d[v] && e[i].w) {
d[v] = d[u] + 1;
q.push(v);
}
}
}
return d[t];
}
int dfs(int u, int flow) {
if (u == t) return flow;
int fl = 0;
for (int i = cur[u]; i; i = e[i].nxt) {
int& v = e[i].v;
cur[u] = i;
if (d[v] == d[u] + 1 && e[i].w) {
int dis = dfs(v, min(flow, e[i].w));
if (dis) {
e[i].w -= dis;
e[i ^ 1].w += dis;
flow -= dis;
fl += dis;
if (!flow) return fl;
}
}
}
return fl;
}
int dinic() {
int ans = 0;
while (bfs(s)) {
memcpy(cur, head, sizeof(head));
ans += dfs(s, inf);
}
return ans;
}
} // namespace Dinic
using Dinic ::add;
namespace SegMentTree {
int id[maxn << 2];
int tag[maxn << 2];
int cnt;
void pushup(int p) {
id[p] = ++cnt;
if (!tag[p << 1]) add(id[p], id[p << 1], inf);
if (!tag[p << 1 | 1]) add(id[p], id[p << 1 | 1], inf);
}
void build(int p, int l, int r) {
if (l == r) {
id[p] = (n + l);
return;
}
int mid = l + r >> 1;
build(p << 1, l, mid);
build(p << 1 | 1, mid + 1, r);
pushup(p);
}
void upd(int p, int a, int b, int l, int r, int v) {
if (a <= l && r <= b) {
tag[p] += v;
return;
}
int mid = l + r >> 1;
if (a <= mid) upd(p << 1, a, b, l, mid, v);
if (b > mid) upd(p << 1 | 1, a, b, mid + 1, r, v);
pushup(p);
}
} // namespace SegMentTree
using SegMentTree ::build;
using SegMentTree ::upd;
struct chg {
int l, r, val;
};
vector<chg> v[maxn];
signed main() {
// code begin.
in >> n >> m;
s = 2 * n + 1, t = 2 * n + 2, SegMentTree ::cnt = 2 * n + 2;
build(1, 1, n);
while (m--) {
int x1, y1, x2, y2;
in >> x1 >> y1 >> x2 >> y2;
v[x1].push_back({ y1, y2, 1 });
v[x2 + 1].push_back({ y1, y2, -1 });
}
rep(i, 1, n) add(s, i, 1), add(i + n, t, 1);
rep(i, 1, n) {
for (auto x : v[i]) {
int l = x.l, r = x.r, v = x.val;
upd(1, l, r, 1, n, v);
}
if (!SegMentTree ::tag[1]) add(i, SegMentTree ::id[1], inf);
}
int ans = Dinic ::dinic();
out << ans << '\n';
return 0;
// code end.
}