#include <bits/stdc++.h>
#define FAST ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);cerr.tie(0)
#define mp make_pair
#define xx first
#define yy second
#define pb push_back
#define pf push_front
#define popb pop_back
#define popf pop_front
#define all(x) x.begin(),x.end()
#define ff(i,a,b) for (int i = a; i < b; i++)
#define fff(i,a,b) for (int i = a; i <= b; i++)
#define bff(i,a,b) for (int i = b-1; i >= a; i--)
#define bfff(i,a,b) for (int i = b; i >= a; i--)
using namespace std;
long double typedef ld;
unsigned int typedef ui;
long long int typedef li;
pair<int,int> typedef pii;
pair<li,li> typedef pli;
pair<ld,ld> typedef pld;
vector<vector<int>> typedef graph;
unsigned long long int typedef ull;
//const int mod = 998244353;
const int mod = 1000000007;
//Note to self: Check for overflow
graph g(500005);
vector<int> listovi;
void dfs(int p, int q)
{
if ((int)g[p].size()==1) listovi.pb(p);
for (auto it : g[p]) if (it!=q) dfs(it,p);
}
int main()
{
FAST;
int n; cin>>n;
ff(i,1,n)
{
int u,v; cin>>u>>v;
g[u].pb(v),g[v].pb(u);
}
int root=-1;
fff(i,1,n) if ((int)g[i].size()!=1) root=i;
dfs(root,-1);
vector<pii> ans;
int m=(listovi).size();
ff(i,0,(m+1)/2) ans.pb({listovi[i],listovi[(i+m/2)%m]});
cout<<(int)ans.size()<<"\n";
for (auto it : ans) cout<<it.xx<<" "<<it.yy<<"\n";
}
//Note to self: Check for overflow
