#include"testlib.h"
#include<bits/stdc++.h>
#include<atcoder/dsu>
using namespace std;
using ll = long long;

const ll Nmin = 2, Nmax = 200'000;

int main(){
    registerValidation();
    
    ll N = inf.readLong(Nmin, Nmax);
    inf.readEoln();

    const ll Vmin = 1, Vmax = N;
    atcoder::dsu d(N);
    for (ll i = 1; i <= N-1; i++){
        ll u = inf.readLong(Vmin, Vmax);
        inf.readSpace();
        ll v = inf.readLong(Vmin, Vmax);
        inf.readEoln();
        inf.ensuref(u < v, "u < v");

        d.merge(u-1, v-1);
    }
    inf.readEof();
    inf.ensuref(d.size(0) == N, "graph is tree");
    return 0;
}