#include <bits/stdc++.h>
#pragma GCC optimize("O3", "unroll-loops")
#define pb emplace_back
#define ins insert
#define ssize(x) (int)x.size()
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define pii pair <int, int>
#define pll pair <ll, ll>
#define pld pair <ld, ld>
#define st first
#define nd second
using namespace std;
using ll = int_fast64_t;
// using lll = __int128_t;
using ld = long double;
const int oo = 1e9 + 7;
const int mod = 1e9 + 7;
void solve(){
int n; cin >> n;
vector <int> deg(n, 0);
for(int i = 1; i < n; i ++){
int a, b; cin >> a >> b;
-- a; -- b;
deg[a] ++;
deg[b] ++;
}
vector <int> leaves;
for(int i = 0; i < n; i ++){
if(deg[i] == 1) leaves.pb(i);
}
cout << (ssize(leaves) + 1) / 2 << '\n';
for(int i = 0; i < ssize(leaves) / 2; i ++){
cout << leaves[i] + 1 << ' ' << leaves[i + ssize(leaves) / 2] + 1 << '\n';
}
if(ssize(leaves) & 1) cout << leaves[0] + 1 << ' ' << leaves.back() + 1 << '\n';
}
signed main(){
ios_base::sync_with_stdio(0); cin.tie(0);
int t; t = 1;
// cin >> t;
while(t --) solve();
return 0;
}
