L - Love Triangle

As you could know there are no male planes nor female planes. However, each plane on Earth likes some other plane. There are n planes on Earth, numbered from 1 to n, and the plane with number i likes the plane with number fi, where 1 ≤ fi ≤ n and fi ≠ i.

We call a love triangle a situation in which plane A likes plane B, plane B likes plane C and plane C likes plane A. Find out if there is any love triangle on Earth.

Input

The first line contains a single integer n (2 ≤ n ≤ 5000) — the number of planes.

The second line contains n integers f1, f2, ..., fn (1 ≤ fi ≤ n, fi ≠ i), meaning that the i-th plane likes the fi-th.

Output

Output «YES» if there is a love triangle consisting of planes on Earth. Otherwise, output «NO».

You can output any letter in lower case or in upper case.

Examples

Input

5
2 4 5 1 3

Output

YES

Input

5
5 5 5 5 1

Output

NO

Note

In first example plane 2 likes plane 4, plane 4 likes plane 1, plane 1 likes plane 2and that is a love triangle.

In second example there are no love triangles.

题解：

水题

代码：

#include <iostream> 
#include <cstdio> 
#include <fstream> 
#include <algorithm> 
#include <cmath> 
#include <deque> 
#include <vector> 
#include <queue> 
#include <string> 
#include <cstring> 
#include <map> 
#include <stack> 
#include <set> 
using namespace std;
int main()
{
	int n;
	cin>>n;
	int a[10001];
	for(int i=1;i<=n;i++)
	{
		cin>>a[i];
	}
	int flag=0;
	for(int i=1;i<=n;i++)
	{
		if(i==a[a[a[i]]])
		{
			cout<<"YES"<<endl;
			flag=1;
			break;
		}
	}
	if(flag==0)
	cout<<"NO"<<endl;
}