https://codeforces.com/contest/1133/problem/B
#include<algorithm>
#include <iostream>
#include <sstream>
#include <cstring>
#include <cstdlib>
#include <string>
#include <vector>
#include <cstdio>
#include <math.h>
#include <queue>
#include <stack>
#include <set>
typedef long long ll;
typedef unsigned long long ull;
#define rep(i,a,n) for (int i = a; i < n; ++i)
#define per(i,a,n) for (int i = n-1; i >= a; --i)
#define SZ(x) ((int)x.size())
using namespace std;
//head
#define maxn 1000006
int a[maxn] = { 0 }, cnt[maxn] = { 0 };
int main()
{
int n, k;
cin >> n >> k;
for (int i = 0; i < n; i++)
{
cin >> a[i];
cnt[a[i] % k] ++;
}
int ans = (cnt[0] / 2);//本来就等于k的两两相组
for (int i = 1; i * 2 <= k; i++)
{
int x = min(cnt[i], cnt[k - i]);
if (i * 2 == k)
ans += x / 2;//去重，与初始化同理
else
ans += x;
}
cout << ans * 2 << endl;
//system("pause");
return 0;
}