#include <bits/stdc++.h>
#define rep(i, a, b) for(int i=(a) ; i<=(b) ; ++i)
#define mp make_pair
#define PB push_back
#define pii pair<int,int>
#define F first
#define S second
#define Task "net"
using namespace std;
const int N=500005;
int n, leaf[N], dem, cnt, s[N], deg[N], root;
vector <int > g[N];
vector <pii > ans;
void setup() {
cin >> n;
rep(i, 2, n) {
int u, v; cin >> u >> v;
g[u].PB(v); g[v].PB(u);
++deg[u]; ++deg[v];
}
}
void DFS(int u, int prv) {
bool check=1;
for(int v:g[u]) {
if(v==prv) continue;
check=0;
DFS(v, u);
}
if(check) leaf[++dem]=u;
}
int main() {
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
//freopen(Task".inp", "r", stdin);
//freopen(Task".out", "w", stdout);
setup();
rep(i, 1, n) {
if(deg[i]>1) { root=i; break; }
}
DFS(root, 0);
rep(i, 1, dem) {
s[++cnt]=leaf[i];
if(cnt>2) {
ans.PB(mp(s[cnt-2], s[cnt]));
s[cnt-2]=s[cnt-1];
cnt-=2;
}
}
if(cnt==2) ans.PB(mp(s[1], s[2]));
else ans.PB(mp(s[1], root));
cout << ans.size() << '\n';
for(auto P:ans) {
cout << P.F << ' ' << P.S << '\n';
}
return 0;
}
