#include <bits/stdc++.h>
#define IO ios::sync_with_stdio(false);cin.tie(0);
#define debug(x) cerr << #x << " = " << (x) << ' '
#define bug(x) cerr << (x) << ' '
#define endl cerr << '\n'
#define all(v) (v).begin(), (v).end()
#define SZ(v) (ll)(v).size()
#define lowbit(x) (x)&-(x)
#define pb emplace_back
#define F first
#define S second
using namespace std;
using ll = long long;
using pll = pair<ll, ll>;
const int N = 5e5+5;
vector<int> g[N], vec;
inline void dfs(int x, int pre)
{
if (SZ(g[x]) == 1) vec.pb(x);
for (int v : g[x]) if (v != pre) dfs(v, x);
}
int main(void)
{ IO
int n, i;
cin >> n;
for (i=0; i < n-1; ++i)
{
int x, y; cin >> x >> y;
g[x].pb(y), g[y].pb(x);
}
dfs(1, 0);
cout << ((SZ(vec)+1)>>1) << '\n';
for (i=1; i < SZ(vec); i+=2) cout << vec[i-1] << ' ' << vec[i] << '\n';
if (SZ(vec) & 1) cout << vec[0] << ' ' << vec.back() << '\n';
return 0;
}
