#include <bits/stdc++.h>
#define int long long
int n;
std::vector<int> adj[500010];
std::vector<int> leaf;
signed main() {
std::ios::sync_with_stdio(false);
std::cin.tie(nullptr);
std::cin >> n;
for(int i=0;i<n-1;i++){
int a,b;
std::cin >> a >> b;
adj[a].push_back(b);
adj[b].push_back(a);
}
for(int i=1;i<=n;i++){
if(adj[i].size()==1)leaf.push_back(i);
}
std::cout << (leaf.size()+1)/2 << '\n';
for(int i=0;i<leaf.size();i++){
std::cout << leaf[i];
if(i%2==0)std::cout << ' ';
else std::cout << '\n';
}
if(leaf.size()%2==1)std::cout << leaf[0] << '\n';
}
