407B - Camino Largo

#include<iostream>
#include<cstring>
#include<algorithm>
#include<cmath>
#include<cstdlib>
#include<climits>
#include<stack>
#include<vector>
#include<queue>
#include<set>
#include<bitset>
#include<map>
//#include<regex>
#include<cstdio>
#include <iomanip>
#pragma GCC optimize(2)
#define up(i,a,b)  for(int i=a;i<b;i++)
#define dw(i,a,b)  for(int i=a;i>b;i--)
#define upd(i,a,b) for(int i=a;i<=b;i++)
#define dwd(i,a,b) for(int i=a;i>=b;i--)
//#define local
typedef long long ll;
typedef unsigned long long ull;
const double esp = 1e-6;
const double pi = acos(-1.0);
const int INF = 0x3f3f3f3f;
const int inf = 1e9;
using namespace std;
ll read()
{
	char ch = getchar(); ll x = 0, f = 1;
	while (ch<'0' || ch>'9') { if (ch == '-')f = -1; ch = getchar(); }
	while (ch >= '0' && ch <= '9') { x = x * 10 + ch - '0'; ch = getchar(); }
	return x * f;
}
typedef pair<int, int> pir;
#define lson l,mid,root<<1
#define rson mid+1,r,root<<1|1
#define lrt root<<1
#define rrt root<<1|1
const int N = 1e3 + 10;
const int mod = 1e9 + 7;
ll dp[N], f[N];
int n, nextt[N];
bool vis[N];
ll add(ll a, ll b)
{
	ll res = a + b;
	if (res >= mod)res -= mod;
	return res;
}
int main()
{
	n = read();
	int pi;
	upd(i, 1, n)
	{
		pi = read();
		nextt[i] = pi;
	}
	dp[1] = 1;
	f[1] = 1;
	upd(i, 2, n)
	{
		if (nextt[i] == i)
		{
			f[i] = 1;
			dp[i] = add(dp[i - 1], 2);
		}
		else {
			int j = i;
			ll sum = 0;
			memset(vis, 0, sizeof(vis));
			while (nextt[j] != j)
			{
				sum++;
				vis[j] =1;
				j = nextt[j];
			}
			up(k, j, i)
			{
				if(!vis[k])
					sum = add(sum, f[k]);
				sum = add(sum, 1);
			}
			f[i] = sum;
			dp[i] = add(dp[i - 1], sum);
			dp[i] = add(dp[i], 1);
		}
	}
	printf("%lld", add(dp[n], 1));
	return 0;
}