#define fast ios_base::sync_with_stdio(0),cin.tie(0),cout.tie(0)
#include <bits/stdc++.h>
using namespace std;
#define sqr 340
#define mid (l+r)/2
#define pb push_back
#define ppb pop_back
#define fi first
#define se second
#define lb lower_bound
#define ub upper_bound
#define ins insert
#define era erase
#define C continue
#define mem(dp,i) memset(dp,i,sizeof(dp))
#define mset multiset
typedef long long ll;
typedef short int si;
typedef long double ld;
typedef pair<int,int> pi;
typedef pair<ll,ll> pll;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<pi> vpi;
typedef vector<pll> vpll;
const ll inf=1e18;
const ld pai=acos(-1);
int n , root ;
vi v[500009] , leaves;
void dfs( int node , int p ) {
if ( v[node].size() == 1 ) leaves . pb ( node ) ;
for ( auto u : v[ node ] ) {
if ( u == p ) C ;
dfs ( u , node ) ;
}
}
int main () {
cin >> n ;
for ( int i = 0 ; i < n-1 ; i ++ ) {
int a , b ;
cin >> a >> b ;
a -- , b -- ;
v[a].pb ( b ) ;
v[b].pb ( a ) ;
}
for ( int i = 0 ; i < n ;i ++ ) {
if ( v[i].size() != 1 ) {
root = i ;
break ;
}
}
dfs(root,root);
vpi ans ;
int num = leaves.size() ;
for ( int i = 0 ; i < num/2 ; i ++ ) {
int j = i + num/2 + (num%2) ;
if ( j >= num ) break ;
int a = leaves[i] ;
int b = leaves[j] ;
ans.pb ( { a+1 , b+1 } );
}
if ( num%2 ) ans.pb ( { leaves[num/2]+1 , leaves[0]+1 } ) ;
cout << ans.size() << endl ;
for ( auto u : ans ) cout << u.fi << " " << u.se << endl ;
}
