Problem: Consider a rooted tree. A rooted tree has one special vertex called the root. All edges are directed from the root. Vertex u is called a child of vertex v and vertex v is called a parent of vertex u if there exists a directed edge from v to u. A vertex is called a leaf if it doesn't have children and has a parent.

Let's call a rooted tree a spruce if its every non-leaf vertex has at least 3 leaf children. You are given a rooted tree, check whether it's a spruce.

The definition of a rooted tree can be found [here](https://goo.gl/1dqvzz).

Input

The first line contains one integer n — the number of vertices in the tree (3 ≤ n ≤ 1 000). Each of the next n - 1 lines contains one integer pi (1 ≤ i ≤ n - 1) — the index of the parent of the i + 1-th vertex (1 ≤ pi ≤ i).

Vertex 1 is the root. It's guaranteed that the root has at least 2 children.

Output

Print "Yes" if the tree is a spruce and "No" otherwise.

Examples

Input

4
1
1
1


Output

Yes


Input

7
1
1
1
2
2
2


Output

No


Input

8
1
1
1
1
3
3
3


Output

Yes

Note

The first example:

<image>

The second example:

<image>

It is not a spruce, because the non-leaf vertex 1 has only 2 leaf children.

The third example:

<image>

Solution (in CPP):

Solution:
#include <bits/stdc++.h>
using namespace std;
long long n, m, answer, cou, _1, _2, _3, _4;
long long visited1[1009], visited[1009];
vector<long long> v[1009];
void dfs(long long root) {
  for (int i = 0; i < v[root].size(); i++) {
    _1 = v[root][i];
    visited[root] = true;
    if (v[_1].size() == 0)
      visited1[root]++;
    else
      dfs(_1);
  }
}
int main() {
  cin >> n;
  for (int i = 2; i <= n; i++) {
    cin >> m;
    v[m].push_back(i);
  }
  dfs(1);
  for (int i = 1; i <= n; i++) {
    if (visited1[i] >= 3 || (visited1[i] == 0 && !visited[i]))
      continue;
    else {
      cout << "NO" << endl;
      return 0;
    }
  }
  cout << "YES" << endl;
}