// In the name of God
// We are everywhere while we are nowhere(Haj NEZAM...)
#include <bits/stdc++.h>
using namespace std;
#define F first
#define S second
#define lc 2 * v
#define rc 2 * v + 1
#define PB push_back
#define MP make_pair
#define ll long long
#define int long long
#define ld long double
#define mid (s + e) / 2
#define pii pair <int , int>
#define _sz(e) (int)e.size()
#define _all(e) e.begin() , e.end()
#define pll pair <long long , long long>
#define piii pair <int , pair <int , int> >
#define FAST ios::sync_with_stdio(0);cin.tie(0)
#define UNI(e) e.resize(unique(_all(e)) - e.begin())
#define kill(e) cout << e << '\n'
#pragma GCC optimize ("O3")
#pragma GCC optimize ("unroll-loops")
const int maxn = 5e5 + 5 , N = 1e6 + 5 , SQ = 450 , base = 800287 , mod = 1e9 + 7 , INF = 1e9 + 5 , lg = 20;
const ld eps = 1e-4;
int n , root;
vector <int> vec;
vector <int> edges[maxn];
void dfs(int v , int p = -1) {
if(_sz(edges[v]) == 1) {
vec.PB(v);
}
for (auto u : edges[v]) {
if(u != p) {
dfs(u , v);
}
}
}
int32_t main() {
FAST;
cin >> n;
for (int i = 0; i < n - 1; ++i) {
int x , y; cin >> x >> y;
x-- , y--;
edges[x].PB(y);
edges[y].PB(x);
}
for (int i = 0; i < n; ++i) {
if(_sz(edges[i]) > 1) {root = i;}
}
dfs(root);
int ans = (_sz(vec) + 1) / 2;
cout << ans << '\n';
for (int i = 0; i < ans; ++i) {
int nxt = min(_sz(vec) - 1 , i + ans);
cout << vec[i] + 1 << ' ' << vec[nxt] + 1 << '\n';
}
}
// Mistakes:
// * Read the problem carefully.
// * Check maxn.
// * Overflows.
