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 f_i, where 1 ≤ f_i ≤ n and f_i ≠ 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.

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

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

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.

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

In second example there are no love triangles.

#include<bits/stdc++.h>

using namespace std;

const int maxn = +;

int main()

{

    int n,a[maxn],ans,j,k;

    while(cin>>n)

    {

        ans=;

        for(int i=;i<=n;i++)

        {

            cin>>a[i];

        }

        for(int i=;i<=n;i++)

        {

            j=a[i];

            k=a[j];

            if(a[k]==i && i!=j && j!=k && i!=k) ans++;

        }

        printf("%s\n",ans?"YES":"NO");

    }

}

#include<bits/stdc++.h>

using namespace std;

const int maxn = +;

int main()

{

    int n,a[maxn],f,ans;

    while(cin>>n)

    {

        for(int i=;i<=n;i++)

            cin>>a[i];

        f=;

        for(int i=;i<=n;i++)

        {

            if(a[a[a[i]]]==i) f=;

        }

        printf("%s\n",f?"YES":"NO");

    }

}