#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int maxn = 5e5+5;
int n;
vector<int> adj[maxn];
int deg[maxn];
int tin[maxn];
int pt = 0;
void dfs(int i, int p) {
tin[i] = pt++;
for (int j: adj[i]) {
if (j == p) continue;
dfs(j,i);
}
}
int main()
{
ios_base::sync_with_stdio(false); cin.tie(NULL);
cin >> n;
for (int i = 0; i < n - 1; i++) {
int a, b; cin >> a >> b;
++deg[a];
++deg[b];
adj[a].push_back(b);
adj[b].push_back(a);
}
vector<int> leafs;
int start = 1;
for (int i = 1; i <= n; i++) {
if (deg[i] == 1) leafs.push_back(i);
if (deg[i] > 1) {
start = i;
}
}
dfs(start,start);
sort(leafs.begin(),leafs.end(),[](auto a, auto b) {
return tin[a] < tin[b];
});
vector<pair<int,int>> ans;
int k = leafs.size();
int m = k/2;
cout << (k+1)/2 << '\n';
for (int i = 0; i < (k+1)/2; i++) {
cout << leafs[i] << ' ' << leafs[(i+m)%k] << '\n';
}
}
