#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];
pii ans[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);
}
int sz = leaf.size();
cout<<(sz+1)/2 <<"\n";
for(int i = 0 ; i < (sz/2); i++)
{
cout << leaf[i] << " " << leaf[i+((sz+1)/2)] << "\n";
}
if(sz%2) cout<< 1 << " " << leaf[sz/2];
}
signed main()
{
ios_base::sync_with_stdio(false);
cin.tie(0); cout.tie(0);
solve();
return 0;
}
