#include<bits/stdc++.h>
using namespace std;
void DBG() { cerr << "]\n"; }
template<class H, class... T> void DBG(H h, T... t) {
cerr << h; if(sizeof...(t)) cerr << ", ";
DBG(t...);
}
#ifdef LOCAL
#define dbg(...) cerr << "[" << #__VA_ARGS__ << "]: [", DBG(__VA_ARGS__)
#else
#define dbg(...) 0
#endif // LOCAL
#define FOR(i,a,b) for(int i = (a) ; i<(b) ; i++)
#define F0R(i,a) FOR(i,0,a)
#define ROF(i,a,b) for(int i = (b)-1 ; i>=(a) ; i--)
#define R0F(i,a) ROF(i,0,a)
#define each(e,a) for(auto &e : (a))
#define sz(v) (int)(v).size()
#define all(v) (v).begin(),(v).end()
#define rall(v) (v).rbegin(),(v).rend()
#define pb push_back
#define tcT template<class T
#define nl "\n"
using ll = long long;
using vi = vector<int>;
using pi = pair<int,int>;
using str = string;
tcT> using V = vector<T>;
tcT> using pqg = priority_queue<T,vector<T>,greater<T>>;
void setIO(string NAME = "") {
cin.tie(0)->sync_with_stdio(0);
if(sz(NAME)) {
freopen((NAME + ".inp").c_str(),"r",stdin);
freopen((NAME + ".out").c_str(),"w",stdout);
}
}
const int MX = 5e5+5;
int N;
vi adj[MX];
vi lfs;
bitset<MX> isleaf;
void solve() {
isleaf.reset();
cin>>N;
F0R(i,N-1) {
int u,v;
cin>>u>>v;
adj[u].pb(v);
adj[v].pb(u);
}
FOR(i,1,N+1) if(sz(adj[i]) == 1) isleaf[i] = 1, lfs.pb(i);
if(sz(lfs)&1) {
cout << sz(lfs)/2+1 << nl;
F0R(i,sz(lfs)/2) {
cout << lfs[i] << " " << lfs[i+sz(lfs)/2+1] << nl;
}
FOR(i,1,N+1) if(!isleaf[i]) {
cout << i << " " << lfs[sz(lfs)/2] << nl;
break;
}
}
else {
cout << sz(lfs)/2 << nl;
F0R(i,sz(lfs)/2) {
cout << lfs[i] << " " << lfs[i+sz(lfs)/2] << nl;
}
}
}
int main() {
setIO();
int t=1;
//cin>>t;
while(t-->0) {
solve();
}
return 0;
}
