hello_2018_b.cpp

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using P = pair<int, int>;


int main(){
    int n;
    cin >> n;

    vector<int> child_cnt(n);
    vector<int> par(n);
    for(int i=1;i<n;i++){
        int p;
        cin >> p;
        par[i] = p - 1;
        child_cnt[p - 1]++;
    }

    vector<int> non_leaf_cnt = child_cnt;
    for(int i=1;i<n;i++){
        if(child_cnt[i] > 0){
            non_leaf_cnt[par[i]]--;
        }
    }

    bool ok = true;
    for(int i=0;i<n;i++){
        if(non_leaf_cnt[i] == 2 || non_leaf_cnt[i] == 1){
            ok = false;
            break;
        }
    }

    if(ok) cout << "Yes" << endl;
    else cout << "No" << endl;

    return 0;
}