#include <bits/stdc++.h>
using namespace std;
int n, a;
vector<int> g[1000001];
int main() {
  cin >> n;
  for (int x = 1; x <= n; x++) {
    cin >> a;
    g[x].push_back(a);
  }
  for (int x = 1; x <= n; x++) {
    for (int y = 0; y < g[x].size(); y++) {
      for (int z = 0; z < g[g[x][y]].size(); z++) {
        for (int k = 0; k < g[g[g[x][y]][z]].size(); k++) {
          if (g[g[g[x][y]][z]][k] == x) {
            cout << "YES";
            return 0;
          }
        }
      }
    }
  }
  cout << "NO";
}

### Prompt

Please formulate a Cpp solution to the following problem:

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 2 and that is a love triangle.

In second example there are no love triangles.

### Response

```cpp
#include <bits/stdc++.h>
using namespace std;
int n, a;
vector<int> g[1000001];
int main() {
  cin >> n;
  for (int x = 1; x <= n; x++) {
    cin >> a;
    g[x].push_back(a);
  }
  for (int x = 1; x <= n; x++) {
    for (int y = 0; y < g[x].size(); y++) {
      for (int z = 0; z < g[g[x][y]].size(); z++) {
        for (int k = 0; k < g[g[g[x][y]][z]].size(); k++) {
          if (g[g[g[x][y]][z]][k] == x) {
            cout << "YES";
            return 0;
          }
        }
      }
    }
  }
  cout << "NO";
}

```