func_code_string: #include <bits/stdc++.h>   using namespace std;   const int maxn = 100100;   int N;   vector<pair<int, int> > ans;   vector<int> E[maxn];   void go(int i, int t) { ans.push_back({i, t}); }   void dfs(int i, int p, int t) {     go(i, t);     int d = (t < E[i].size());     if (!d) t -= E[i].size(), go(i, t);     for (auto &j : E[i])       if (j != p) {         t++;         dfs(j, i, t);         go(i, t);         if (d && t == E[i].size()) t -= E[i].size(), go(i, t);       }   }   int main() {     ios_base::sync_with_stdio(false);     cin.tie(NULL);     cin >> N;     int u, v;     for (int i = 1; i < N; i++) {       cin >> u >> v;       E[u].push_back(v);       E[v].push_back(u);     }     go(1, 0);     int t = 0;     for (auto &i : E[1]) t++, dfs(i, 1, t), go(1, t);     cout << ans.size() <<   n ;     for (auto &i : ans) cout << i.first <<     << i.second <<   n ;   }   