仔细想想，一颗真正有分叉的树怎么可能一笔画，所以只能是退化成一条链的树

#include<bits/stdc++.h>
using namespace std;

int main(){
    int n; cin >> n;
    vector<int> d(n + 5);
    for(int i = 1; i < n; i ++){
        int u, v; cin >> u >> v;
        d[u] ++, d[v] ++;
    }
    if(n == 2)  cout << "1 2" << endl;
    else{
        vector<int> res;
        for(int i = 1; i <= n; i ++)
            if(d[i] == 1)   res.push_back(i);
            else if(d[i] != 2){
                cout << -1 << endl;
                return 0;
            }
        cout << res[0] << ' ' << res[1] << endl;
    }
}