#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define N 600005
#define ff first
#define ss second
#define pb push_back
#define sz(s) (int)s.size()
#define rep(c, a, b) for(c = a; c <= b; c++)
//mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
ll n, t, out[N], mx, nd;
vector <int> v[N], answer;
vector <pair<int,int>> ans;
map <int,int> vis, vip;
void solve(int x,int answer, int cnt) {
vis[x] = 1;
for(auto i:v[x]) {
if(vis[i]) continue;
solve(i,answer,cnt + 1);
}
if(sz(v[x]) == 1 && vip[x] == 0 && cnt > mx) {
mx = cnt;
nd = x;
}
}
int main () {
ios::sync_with_stdio(0);cin.tie(0);
cin >> n;
for(int i = 1; i < n; i++) {
int x, y;
cin >> x >> y;
v[x].pb(y);
v[y].pb(x);
}
for(int i = 1;i<=n;i++) {
if(sz(v[i]) == 1) answer.pb(i);
}
cout << (sz(answer) + 1) / 2 << '\n';
if(sz(answer) % 2 != 0) {
t = answer[sz(answer)- 1];
answer.pop_back();
}
for(auto i : answer) {
if(vip[i]) continue;
vis.clear();
mx = nd = 0;
solve(i, i, 0);
vip[i] = 1;
vip[nd] = 1;
cout << i << " " << nd << '\n';
}
if(!t) return 0;
vip.clear();
solve(t,t,0);
cout << t << " " << nd << '\n';
}
