#include <bits/stdc++.h>
#define ll long long
#define fi first
#define se second
#define pb push_back
#define ii pair<ll, ll>
#define all(a) a.begin(), a.end()
#define iii pair<ll,ii>
using namespace std;
const ll N =1e6+5;
const ll mod = 998244353;
const ll inf=1e18;
ll n,i,j,m,q,k,t,x,y;
vector<ll> v[N],ans;
ll timedfs=0;
void dfs(ll u,ll p)
{
++timedfs;
if(v[u].size()==1) ans.pb(u);
for(auto x:v[u])
if(x!=p) dfs(x,u);
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
cout.tie(nullptr);
cin>>n;
for(i=1;i<n;i++)
{
cin>>x>>y;
v[x].pb(y);
v[y].pb(x);
}
for(i=1;i<=n;i++)
if(v[i].size()>1)
{
dfs(i,0);
// solve
ll sz=ans.size();
cout<<(sz+1)/2<<'\n';
for(i=0;i+(sz+1)/2<sz;i++)
cout<<ans[i]<<" "<<ans[i+(sz+1)/2]<<'\n';
if(sz&1) cout<<ans[sz/2]<<" "<<i<<'\n';
return 0;
}
return 0;
}
/*
*/
