#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define MAXN 500005
#define FOR(i, a, b) for(ll i = a; i <= b; i++)
ll n;
pair<ll, ll> dp[MAXN];
vector<ll> adj[MAXN];
vector<pair<ll, ll>> cn[MAXN];
void dfs(ll v, ll p){
if(adj[v].size() == 1 && adj[v][0] == p){
dp[v] = {1, v};
return;
}
dp[v] = {2, -1};
// cout << "for " << v << "(" << dp[v].first << ")" << endl;
for(ll v2 : adj[v]) if(p != v2){
// cout << "for " << v << " going to " << v2 << "(" << dp[v].first << ")" << endl;
dfs(v2, v);
if(dp[v].first == 2){
// cout << " option -1" << endl;
swap(cn[v], cn[v2]), dp[v] = dp[v2];
continue;
}
if(dp[v].first == 0){
if(dp[v2].first == 0){
// cout << " go option 0" << endl;
pair<ll, ll> bk = cn[v].back(), bk2 = cn[v2].back();
cn[v].pop_back(), cn[v2].pop_back();
cn[v].push_back({bk.first, bk2.first});
cn[v2].push_back({bk.second, bk2.second});
}else{
// cout << " go option 1" << endl;
dp[v] = dp[v2];
}
}else{
if(dp[v2].first == 0){
// cout << " go option 2" << endl;
pair<ll, ll> bk = cn[v2].back();
cn[v2].pop_back();
cn[v2].push_back({bk.first, dp[v].second});
dp[v].second = bk.second;
}else{
// cout << " go option 3" << endl;
cn[v].push_back({dp[v].second, dp[v2].second});
dp[v].first = 0;
}
}
if(cn[v].size() < cn[v2].size()) swap(cn[v], cn[v2]);
}
}
int main(){
cin >> n;
FOR(i, 1, n - 1){
ll a, b; cin >> a >> b;
adj[a].push_back(b), adj[b].push_back(a);
}
dfs(1, -1);
/*FOR(i, 1, n){
cout << i << ": " << dp[i].first << " " << dp[i].second << endl;
}
*/
ll r = dp[1].first + (adj[1].size() == 1 && dp[1].first == 0);
FOR(i, 1, n) r += (ll)cn[i].size();
cout << r << endl;
bool x1 = (adj[1].size() == 1 && dp[1].first == 0);
FOR(i, 1, n){
for(pair<ll, ll> pi : cn[i]){
if(x1) {
cout << pi.first << " " << 1 << endl;
cout << pi.second << " " << 1 << endl;
x1 = false;
continue;
}
cout << pi.first << " " << pi.second << endl;
}
}
if(dp[1].first) cout << dp[1].second << " " << 1 << endl;
}
