#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <bits/stdc++.h>
#define fi first
#define se second
#define pb push_back
#define sz(a) (int)a.size()
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define ff(i,a,b) for(int i=a;i<=b;i++)
#define fb(i,b,a) for(int i=b;i>=a;i--)
using namespace std;
using namespace __gnu_pbds;
typedef long long ll;
typedef pair<int,int> pii;
const int maxn = 500005;
const int inf = 1e9 + 5;
template<typename T>
using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
// os.order_of_key(k) the number of elements in the os less than k
// *os.find_by_order(k) print the k-th smallest number in os(0-based)
int n;
int deg[maxn];
int main()
{
ios::sync_with_stdio(false);
cout.tie(nullptr);
cin.tie(nullptr);
cin >> n;
ff(i,1,n - 1){
int u, v;
cin >> u >> v;
deg[u] += 1, deg[v] += 1;
}
vector<int> res;
ff(i,1,n)if(deg[i] == 1)res.pb(i);
int len = sz(res);
cout << (len + 1) / 2 << endl;
for(int i = 1; i < len; i += 2){
cout << res[i - 1] << " " << res[i] << '\n';
}
if(len % 2 == 1)cout << res[len - 2] << " " << res[len - 1] << '\n';
return 0;
}
/**
// probati bojenje sahovski ili slicno
**/
