#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define fi first
#define se second
#define ldb long double
#define pii pair<int, int>
#define bend(v) v.begin(), v.end()
const int N = 1e6 + 5, M = 1e6 + 5;
const int mod = 1e9 + 7;
const int base = 311;
const int inf = INT_MAX;
const ll INF = LLONG_MAX;
int n, in[N], h[N];
vector<int> adj[N], v;
int d[N];
void dfs(int u, int par){
if(in[u] == 1) v.push_back(u);
for(int v : adj[u]){
if(v == par) continue;
dfs(v, u);
}
}
bool comp(int x, int y){
return h[x] > h[y];
}
void solve(){
cin>>n;
for(int i = 1; i < n; i++){
int x, y; cin>>x>>y;
adj[x].push_back(y);
adj[y].push_back(x);
in[x]++; in[y]++;
}
dfs(1, 0);
int k = ((int)v.size() + 1) / 2;
// for(int x : v) cout<<x<<" ";
// cout<<'\n';
// cout<<k<<'\n';
cout<<k<<'\n';
for(int i = 0; i < k; i++){
cout<<v[i]<<" "<<v[(i + k) % ((int)v.size())]<<'\n';
}
// if((int)v.size() % 2 == 1) cout<<v.back()<<" "<<1<<'\n';
}
signed main(){
// freopen(".inp", "r", stdin);
// freopen(".out", "w", stdout);
ios_base::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
int tc = 1;
// cin>>tc;
while(tc--) solve();
}
