#include <bits/stdc++.h>
//#define DEBUG 1106
#define int long long
#define ll long long
#define ld long double
#define pb push_back
#define p_q priority_queue
#define m_p make_pair
#define pii pair<int,int>
#define endl '\n'
#define INIT ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define FOR(i,a,b) for(int i = a; i <= b; i++)
#define forn(i,n) for (int i = 0; i < n; i++)
#define forn1(i,n) for (int i = 1; i <= n; i++)
#define all(x) x.begin(),x.end()
#define ft first
#define sd second
#define lowbit(x) (x&(-x))
#define chmax(x,y) x=max(x,y)
#define chmin(x,y) x=min(x,y)
#ifdef DEBUG
#define debug(x) cout << #x << ": " << x << endl;
#else
#define debug(x) 1106;
#endif
using namespace std;
const int N = 6e5+5;
const int M = 2005;
const int inf = 1e9;
const int INF = 1e18;
const int MOD = 1e9+7;
int a[N];
vector<int> G[N];
vector<int> ret;
void dfs(int u, int par) {
for(auto v: G[u]) {
if(v!=par) dfs(v,u);
}
if(G[u].size()==1) ret.pb(u);
}
signed main() {
INIT
#ifdef DEBUG
freopen("input.txt", "r", stdin);
#endif
///////////
int n;
cin >> n;
forn(i,n-1) {
int x, y;
cin >> x >> y;
G[x].pb(y);
G[y].pb(x);
a[x]++; a[y]++;
}
forn1(i,n) {
if(a[i]>1) {
dfs(i,0);
break;
}
}
int m = ret.size();
cout << (m+1)/2 << endl;
forn(i,m/2) {
cout << ret[i] << ' ' << ret[i+m/2] << endl;
}
if(m%2==1) cout << ret[0] << ' ' << ret[m-1];
}
