#include <bits/stdc++.h>
using namespace std;
int n;
vector<vector<int>> a;
vector<int>gr,frunz;
void dfs(int nod,int rad) {
bool frun=true;
for (auto f:a[nod]) {
if (f==rad) continue;
frun=false;
dfs(f,nod);
}
if (frun) frunz.push_back(nod);
}
int main() {
cin>>n;
a.resize(n+1);
gr.resize(n+1);
int x,y;
for (int i=1;i<n;i++) {
cin>>x>>y;
gr[x]++;
gr[y]++;
a[x].push_back(y);
a[y].push_back(x);
}
for (int i=1;i<=n;i++) {
if (gr[i]>1) {
dfs(i,0);
break;
}
}
int cf=frunz.size(),ans=(cf+1)/2,skip=cf/2;
cout<<ans<<'\n';
for (int i=0;i<ans;i++) cout<<frunz[i]<<" "<<frunz[(i+skip)%cf]<<endl;
return 0;
}
