#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';
}
