#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define pb push_back
#define fi first
#define si second
#define ar array
typedef pair<int,int> pi;
typedef tuple<int,int,int> ti;
template<typename T> bool chmin(T &a, T b){return (b < a) ? a = b, 1 : 0;}
template<typename T> bool chmax(T &a, T b){return (b > a) ? a = b, 1 : 0;}
mt19937 rng(chrono::system_clock::now().time_since_epoch().count());
void debug_out() {cerr<<endl;}
template <typename Head, typename... Tail>
void debug_out(Head _H, Tail... _T) {cerr<<" "<<to_string(_H);debug_out(_T...);}
#define debug(...) cerr<<"["<<#__VA_ARGS__<<"]:",debug_out(__VA_ARGS__)
const int MAXN = 500010;
int n;
vector<int> g[MAXN];
vector<int> leaf;
void dfs(int x, int p) {
if ((int)g[x].size() == 1) leaf.pb(x);
for (auto i: g[x]) {
if (i == p) continue;
dfs(i, x);
}
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
cin.exceptions(ios::badbit | ios::failbit);
cin >> n;
for (int i = 1; i < n; ++i) {
int u, v; cin >> u >> v;
g[u].pb(v);
g[v].pb(u);
}
dfs(1, 1);
int ans = ((int)leaf.size() + 1) / 2;
cout << ans << '\n';
if ((int)leaf.size() % 2) leaf.pb(leaf.front());
int j = ans;
for (int i = 0; i < ans; ++i) {
cout << leaf[i] << ' ' << leaf[j++] << '\n';
}
return 0;
}
