#include<bits/stdc++.h> using namespace std; vector<pair<int,int>> ans; vector<int> node; const int N = 5e5 + 7; vector<int> g[N]; int deg[N],n; void dfs(int u, int p){ if(deg[u] == 1){ if(node.size() >= 2) ans.push_back({u,node.back()}), node.pop_back(); else node.push_back(u); } for(int v : g[u]) if(v != p){ dfs(v,u); } } int main(){ ios_base::sync_with_stdio(0); cin.tie(0);cout.tie(0); cin >> n; for(int i = 1; i < n; i++){ int u,v; cin >> u >> v; g[u].push_back(v); g[v].push_back(u); deg[u]++; deg[v]++; } int root = 1; for(int i = 1; i <= n; i++) if(deg[i] != 1) root = i; dfs(root,0); if(node.size() == 2){ ans.push_back({node[0],node[1]}); node.clear(); } while(!node.empty()){ ans.push_back({node.back(),root}); node.pop_back(); } cout << ans.size() <<'\n'; for(auto [u,v] : ans) cout << u <<' ' << v << '\n'; }