#include <bits/stdc++.h>
using namespace std;
long long n, u, v, num[(long long)(1e5 + 5)], leaf[(long long)(1e5 + 5)];
double ans = 0, cnt = 0;
bool vis[(long long)(1e5 + 5)];
vector<long long> graph[(long long)(1e5 + 5)];
void dfs(long long x, long long parent) {
  if (vis[x]) return;
  vis[x] = 1;
  if (graph[x].size() == 0) {
    num[parent]++;
    leaf[x] = 1;
  }
  for (auto s : graph[x])
    if (!vis[s]) dfs(s, x);
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cin >> n;
  for (long long i = 2; i < n + 1; i++) {
    cin >> u;
    graph[u].push_back(i);
  }
  dfs(1, 0);
  for (long long i = 1; i <= n; i++) {
    if (leaf[i] == 0 && num[i] < 3) {
      cout << "NO";
      return 0;
    }
  }
  cout << "YES";
  return 0;
}
