#include <bits/stdc++.h>
using namespace std;
#define x first
#define y second
#define lg length()
#define pb push_back
#define INF 2000000005
#define LINF 1000000000000000005
#define all(x) (x).begin(), (x).end()
#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define sz(x) (int)(x).size()
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef vector<int> vi;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
int rand(int l,int r){return uniform_int_distribution<int>(l,r)(rng);}
#define int ll
int n,x,y,dp[500005][2],u[500005],v[500005];
vector <pii> ans;
vector <int> g[500005];
void DFS(int nod, int par){
int sum = 0, p = 0;
int A = 0, B = 0;
for(int i : g[nod]){
if(i == par) continue;
DFS(i, nod);
if(dp[i][1] <= dp[i][0]){
sum += dp[i][1];
p++;
if(B) ans.pb({B, u[i]}), B = 0;
else if(A) B = u[i];
else A = u[i];
}
else{
sum += dp[i][0];
p+=2;
if(B) ans.pb({B, u[i]}), B = v[i];
else if(A) ans.pb({A, u[i]}), A = v[i];
else A = u[i], B = v[i];
}
}
dp[nod][1] = sum + p / 2;
dp[nod][0] = sum + (p - 1) / 2;
if(par == -1){
if(B) ans.pb({A,B});
else if(A) ans.pb({A,nod});
}
else if(dp[nod][1] <= dp[nod][0]){
if(B) ans.pb({B, nod});
if(!A) A = nod;
u[nod] = A;
}
else{
if(!A) A = nod;
if(!B) B = nod;
u[nod] = A, v[nod] = B;
}
}
int32_t main(){
ios_base :: sync_with_stdio(0); cin.tie(); cout.tie();
#ifdef LOCAL_DEFINE
ifstream cin("input.txt");
#endif
cin >> n;
for(int i=1;i<n;i++){
cin >> x >> y;
g[x].pb(y);
g[y].pb(x);
}
int root = -1;
for(int i=1;i<=n;i++){
if(sz(g[i]) > 1) root = i;
}
DFS(root,-1);
cout << sz(ans) << '\n';
for(pii i : ans) cout << i.x << ' ' << i.y << '\n';
}
