#pragma GCC optimize("Ofast,unroll-loops,fast-math")
#include<bits/stdc++.h>
using namespace std;
typedef long long ll ;
#define pll pair<ll , ll >
#define all(x) (x).begin(),(x).end()
#define SZ(x) (ll)(x).size()
#define X first
#define Y second
#define mp make_pair
#define pii pair<int , int>
#define vec vector
#define file_io freopen("input.txt", "r", stdin);freopen("output.txt", "w", stdout);
#define migmig ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define pb push_back
#define ld long double
// BIG p : 1000000000000037 , 100000000003
ll poww(ll a, ll b, ll md) {
return (!b ? 1 : (b & 1 ? a * poww(a * a % md, b / 2, md) % md : poww(a * a % md, b / 2, md) % md));
}
const int maxn = 5000*100+5 ;
const ll inf = 9223372036854775807 ;
const ll mod = 1e9 + 7 ;
const int lg = 20 ;
int n , nl , st[maxn] , cnt , mark[maxn];
vec<pii> l ;
vec<int> adj[maxn] ;
void dfs(int v ){
st[v] = cnt ++;
mark[v] = 1 ;
for(auto u : adj[v]) if(!mark[u]) dfs(u) ;
}
int main()
{
migmig ;
cin>>n ;
for(int i = 1 ; i < n ; i ++ ){
int u , v ;
cin>>u>>v ;
adj[u].pb(v) ;
adj[v].pb(u) ;
}
for(int i = 1 ; i <= n ; i ++ ){
if(adj[i].size() != 1){
dfs(i) ;
break ;
}
}
vec<pii> v ;
for(int i = 1 ; i <= n ; i ++ ){
if(SZ(adj[i]) == 1){
nl ++ ;
v.pb({st[i] , i}) ;
}
}
sort(all(v)) ;
cout<<(nl + 1 ) / 2 <<endl ;
nl = (nl + 1) / 2 ;
for(int i = 0 ; i + nl < SZ(v) ; i ++ ){
cout<<v[i].Y <<" " << v[i + nl].Y << endl ;
}
if(SZ(v) % 2 == 1){
cout<<v[nl-1].Y <<" " << v[0].Y << endl ;
}
}
