#include <bits/stdc++.h>
#define ll long long
#define all(lpv) lpv.begin(), lpv.end()
#define pot(x, y) lower_bound(x.begin(), x.end(), y) - x.begin() + 1
using namespace std;
#define lpv
#ifndef lpv
#include "AC.h"
#endif // lpv
//#define int long long
const int N = 1e6 + 5;
int n, a[N];
vector<int> p[N];
int ans = 0, f[N], g[N], pa[22][N], in[N], en[N], demin;
void pre(int u,int v) {
in[u] = ++demin;
for(int j = 1; j <= 20; j ++) pa[j][u] = pa[j - 1][pa[j - 1][u]];
for(auto j : p[u]) if(j != v) {
pa[0][j] = u;
pre(j, u);
}
en[u] = demin;
}
bool kt(int u,int v) {
return in[u] <= in[v] && in[v] <= en[u];
}
int LCA(int u,int v) {
if(kt(u, v)) return u;
int kq = u;
for(int i = 20; i >= 0; i --) if(kt(pa[i][u], v)) kq = pa[i][u];
else u = pa[i][u];
return kq;
}
vector<pair<int,int>> kq;
void dfs(int u,int v) {
if((int)p[u].size() == 1 && u != 1) {
f[u] = u;
ans++;
return;
}
for(auto j : p[u]) if(j != v) {
dfs(j, u);
if(!f[u]) {
f[u] = f[j];
g[u] = g[j];
continue;
}
if(!g[u]) {
if(g[j]) {
kq.push_back({f[u], f[j]});
ans--;
f[u] = g[j];
} else {
g[u] = f[j];
}
} else {
kq.push_back({f[j], g[u]});
g[u] = g[j];
ans--;
}
}
if(u == 1) {
if(g[u]) {
if(LCA(g[u], f[u]) == u) {
ans--;
kq.push_back({g[u], f[u]});
} else {
kq.push_back({u, f[u]});
kq.push_back({u, g[u]});
}
} else {
kq.push_back({u, f[u]});
}
}
cerr << u << " " << f[u] << " " << g[u] << "\n";
}
#ifdef lpv
signed main() {
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define task "v"
if(fopen(task ".inp","r")) {
freopen(task ".inp","r",stdin);
freopen(task ".out","w",stdout);
}
cin >> n;
for(int i = 1; i < n; i ++) {
int x, y; cin >> x >> y;
p[x].push_back(y);
p[y].push_back(x);
}
dfs(1, 0);
cout << ans << "\n";
for(auto [x, y] : kq) cout << x << " " << y << "\n";
}
#endif // lpv
