#include <bits/stdc++.h>
using namespace std;
int n;
queue<int> q;
vector<int> v[1999];
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cin >> n;
  for (int i = 2; i <= n; i++) {
    int a;
    cin >> a;
    v[a].push_back(i);
  }
  q.push(1);
  int ok = 1;
  while (!q.empty()) {
    int cou = 0, sep = 0;
    int k = q.front();
    q.pop();
    for (auto x : v[k]) {
      sep = 1;
      if (v[x].empty()) {
        cou++;
      }
      q.push(x);
    }
    if (sep) {
      if (cou < 3) {
        ok = 0;
        break;
      }
    }
  }
  if (ok) {
    cout << "YES";
  } else {
    cout << "NO";
  }
}
