#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define N 600005
#define ff first
#define ss second
#define pb push_back
#define sz(s) (int)s.size()
#define rep(c, a, b) for(c = a; c <= b; c++)
//mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
ll n, t, out[N],vip[3000][3000], cnt;
vector <int> v[N], ans;
void find(int x) {
out[x] = 1;
cnt++;
for(auto i:v[x]) {
if(vip[x][i] == 1 || out[i] == 1) continue;
find(i);
}
}
void solve() {
bool tr = 0;
for(int i = 1; i <= n; i++) {
for(auto j:v[i]) {
for(int k = 1; k <= n; k++) {
out[k] = 0;
}
vip[i][j] = vip[j][i] = 1;
cnt = 0;
find(1);
vip[i][j] = vip[j][i] = 0;
if(cnt != n) {
tr = 1;
break;
}
}
if(tr) break;
}
if(!tr) {
cout << (sz(ans) + 1) / 2 << '\n';
for(int i = 0;i<sz(ans) - 1;i++) {
cout << ans[i] << " " << ans[i+1] << '\n';
i++;
}
if(sz(ans)%2) {
cout << ans[0] << " " << ans[sz(ans) - 1] << '\n';
}
exit(0);
}
}
int main () {
ios::sync_with_stdio(0);cin.tie(0);
cin >> n;
for(int i = 1; i < n; i++) {
int x, y;
cin >> x >> y;
v[x].pb(y);
v[y].pb(x);
}
for(int i = 1;i<=n;i++) {
if(sz(v[i]) == 1) ans.pb(i);
}
do{
for(int i = 0;i<sz(ans) - 1;i++) {
v[ans[i]].pb(ans[i+1]);
v[ans[i+1]].pb(ans[i]);
i++;
}
if(sz(ans)%2) {
v[ans[0]].pb(ans[sz(ans) - 1]);
v[ans[sz(ans) - 1]].pb(ans[0]);
}
solve();
for(int i = 0;i<sz(ans) - 1;i++) {
v[ans[i]].pop_back();
v[ans[i+1]].pop_back();
i++;
}
if(sz(ans)%2) {
v[ans[0]].pop_back();
v[ans[sz(ans) - 1]].pop_back();
}
}while(next_permutation(ans.begin(),ans.end()));
}
