abckjs

#include <iostream>
#include <utility>
#include <vector>
#include <algorithm>

using namespace std;

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

    vector<pair<int, int>> segment;
    vector<int> count(n, 0);
    vector<int> level(n, 1);
    vector<int> leaf;

    for (int i = 0; i < n - 1; ++ i) {
        int parents, child;
        cin >> parents >> child;

        pair<int, int> p = make_pair(parents, child);
        segment.push_back(p);
        count[parents] ++;
        level[child] = level[parents] + 1;
    }
    
    for (int i = 0; i < count.size(); ++ i) {
        if (count[i] == 0) {
            leaf.push_back(level[i]);
        }
    }

    sort(leaf.begin(), leaf.end());
    if (leaf[leaf.size() - 1] - leaf[0] <= 1) {
        cout << "yes";
    } else {
        cout << "no";
    }

    return 0;


}