#include<bits/stdc++.h>
using namespace std;
#define int long long
#define X first
#define Y second
#define pb push_back
const int N = 5e5 + 1;
typedef pair<int,int> ii;
vector<int> g[N];
vector<ii> res;
ii dfs(int u,int p) {
if (g[u].size() == 1) return ii(u,0);
ii ans = ii(0,0);
for(int v : g[u])
if (v != p) {
ii cur = dfs(v,u);
if (!ans.X) {
ans = cur;
continue;
}
if (!ans.Y) {
if (cur.Y) {
res.pb({ans.X,cur.X});
ans.X = cur.Y;
}
else
ans.Y = cur.X;
continue;
}
res.pb({ans.Y,cur.X});
ans.Y = cur.Y;
}
return ans;
}
signed main() {
ios_base::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
int n; cin >> n;
for(int i = 1 ; i < n ; ++i) {
int x, y; cin >> x >> y;
g[x].push_back(y);
g[y].push_back(x);
}
for(int i = 1 ; i <= n ; ++i)
if (g[i].size() > 1) {
ii cur = dfs(i,0);
if (!cur.Y) cur.Y = i;
res.pb({cur.X,cur.Y});
break;
}
cout << res.size() << "\n";
for(ii e : res) cout << e.X << " " << e.Y << "\n";
}
