#include <bits/stdc++.h>
using namespace std;
#define int long long
//#define pb push_back
int inf = 1e18;
const int mod = 1e9 + 7;
const int N = 1e5 + 5;
void solve(){
int n;
cin >> n;
vector<vector<int>> g(n+1);
for(int i = 1; i < n; i ++ ) {
int a, b;
cin >> a >> b;
g[a].push_back(b);
g[b].push_back(a);
}
int root = 1;
while(g[root].size() == 1) root ++ ;
vector<array<int,2>> ans;
function<vector<int>(int,int)> dfs = [&] (int ps, int pr){
if(g[ps].size() == 1) {
vector<int> res = {ps};
return res;
};
vector<int> cur;
for(int to : g[ps])
if(to != pr){
vector<int> res = dfs(to, ps);
if(cur.size() == 0) cur = res;
else {
if(cur.size() < res.size())swap(cur, res);
while(cur.size() > 1 && res.size()) {
ans.push_back({res.back(), cur.back()});
cur.pop_back();
res.pop_back();
}
for(int i:res)cur.push_back(i);
}
}
//cout << ":" << ps << '\n';
//for(auto i : cur)cout << i << ' ';
//cout << '\n';
return cur;
};
vector<int> res = dfs(root, root);
for(int i = 1; i < res.size(); i += 2)
ans.push_back({res[i], res[i-1]});
if(res.size()%2 == 1)
ans.push_back({res.back(), ans.back()[1]});
cout << ans.size() << '\n';
for(auto [a, b] : ans)cout << a << ' ' << b << '\n';
};
signed main(){
ios_base::sync_with_stdio(false);
cin.tie(nullptr); cout.tie(nullptr);
int tt = 1;
//cin >> tt;
while(tt -- ){
solve();
};
};
