#include <bits/stdc++.h>
#define pii pair <int , int>
#define fi first
#define se second
using namespace std;
const int INF = 1e9;
const int maxn = 5e5 + 7;
int n , child[maxn];
vector <int> g[maxn];
vector <int> leaf;
void dfs(int u , int p)
{
for(int v: g[u])
{
if(v == p) continue;
child[u]++;
dfs(v , u);
}
if(child[u] == 0)
{
leaf.push_back(u);
}
}
void solve()
{
cin >> n;
for(int i = 1; i < n; i++)
{
int u , v; cin >> u >> v;
g[u].push_back(v);
g[v].push_back(u);
}
dfs(1 , 1);
if(child[1] == 1)
{
leaf.push_back(1);
}
cout << ((int)leaf.size() + 1)/2 << '\n';
int l = 0;
int r = leaf.size() - 1;
while(l < r)
{
cout << leaf[l] << ' ' << leaf[r] << '\n';
l++;
r--;
}
if((int)leaf.size() % 2 == 1)
{
cout << leaf[l] << ' ' << leaf[0] << '\n';
}
}
signed main()
{
ios_base::sync_with_stdio(false);
cin.tie(0); cout.tie(0);
solve();
return 0;
}
