#include <bits/stdc++.h>
//#pragma GCC optimize("Ofast")
/*#pragma comment(linker, "/stack:200000000")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")*/
#pragma GCC optimize("O2")
/*#pragma GCC optimize("unroll-loops")
#pragma GCC target("avx,avx2,sse,sse2,fma")*/
using namespace std;
using ll = long long int;
#define F first
#define S second
#define pb push_back
#define mp make_pair
#define lc v<<1
#define rc v<<1|1
#define fast_io ios::sync_with_stdio(false);cin.tie(nullptr);cout.tie(nullptr);
const int N=5e5+10,LN=20,M=1e5+4,SQ=350,B=737,inf=1e9;
const ll INF=1e18;
const int MH=1000696969,MOD=1000000007 /*998244353*/;
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
using pll=pair<ll,ll>;
using pii=pair<int,int>;
#define ordered_set tree<pll, null_type,less<pll>, rb_tree_tag,tree_order_statistics_node_update>
ll pow(ll x, ll y, ll mod){
ll ans=1;
while (y != 0) {
if (y & 1) ans = ans * x % mod;
y >>= 1;
x = x * x % mod;
}
return ans;
}
ll n;
vector<ll> adj[N],le;
void dfs(ll v, ll p){
if(adj[v].size()==1) le.pb(v);
for(ll u : adj[v]){
if(u!=p) dfs(u,v);
}
}
int main(){
fast_io;
cin >> n;
for(ll i=1; i<n; i++){
ll v,u;
cin >> v >> u;
adj[v].pb(u);
adj[u].pb(v);
}
dfs(1,0);
ll k=(le.size()+1)/2,t=le.size()/2;
cout << k << '\n';
for(ll i=0; i<k; i++){
cout << le[i] << ' ' << le[i+t] << '\n';
}
return 0;
}
