#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef long double ld;
#define rep(a, b) for(int a = 0; a < (b); ++a)
#define st first
#define nd second
#define pb push_back
#define all(a) a.begin(), a.end()
const int LIM=5e5+7;
vector<int>V[LIM];
vector<pair<int,int>>T;
int tr[4*LIM], pre[LIM], post[LIM], jaki[LIM], lpre, N=1, ost=-1;
void DFS(int x, int o) {
++lpre;
jaki[lpre]=x;
pre[x]=lpre;
for(auto i : V[x]) if(i!=o) DFS(i, x);
post[x]=lpre;
}
void upd(int v) {
v+=N;
while(v) {
--tr[v];
v/=2;
}
}
int cnt(int l, int r) {
l+=N; r+=N;
int ans=tr[l];
if(l!=r) ans+=tr[r];
while(l/2!=r/2) {
if(l%2==0) ans+=tr[l+1];
if(r%2==1) ans+=tr[r-1];
l/=2; r/=2;
}
return ans;
}
int zejdz(int v) {
if(v>=N) {
upd(v-N);
return jaki[v-N];
}
if(tr[2*v]>0) return zejdz(2*v);
return zejdz(2*v+1);
}
int znajdz(int l, int r) {
l+=N; r+=N;
vector<int>A, B;
A.pb(l);
if(l!=r) B.pb(r);
while(l/2!=r/2) {
if(l%2==0) A.pb(l+1);
if(r%2==1) B.pb(r-1);
l/=2; r/=2;
}
for(auto i : A) if(tr[i]>0) return zejdz(i);
reverse(all(B));
for(auto i : B) if(tr[i]>0) return zejdz(i);
return -1;
}
void DFS2(int x, int o, vector<int>&P) {
int p=cnt(pre[x], post[x]);
bool t=false;
for(auto i : V[x]) if(i!=o) {
int z=cnt(pre[i], post[i]);
if(2*z>p+P.size()) t=true;
}
if(t) {
int b=P.size();
for(auto i : V[x]) if(i!=o && 2*cnt(pre[i], post[i])<=p+b) {
int a=znajdz(pre[i], post[i]);
while(a!=-1) {
P.pb(a);
a=znajdz(pre[i], post[i]);
}
}
for(auto i : V[x]) if(i!=o && cnt(pre[i], post[i])) DFS2(i, x, P);
return;
}
priority_queue<pair<ll,ll>>q;
if(P.size()) q.push({P.size(), LIM});
for(auto i : V[x]) if(i!=o && cnt(pre[i], post[i])) q.push({cnt(pre[i], post[i]), i});
while(q.size()>1) {
auto a=q.top(); q.pop();
auto b=q.top(); q.pop();
--a.st;
if(a.st) q.push(a);
--b.st;
if(b.st) q.push(b);
int r, t;
if(a.nd==LIM) {
r=P.back(); P.pop_back();
} else r=znajdz(pre[a.nd], post[a.nd]);
if(b.nd==LIM) {
t=P.back();
P.pop_back();
} else t=znajdz(pre[b.nd], post[b.nd]);
T.pb({r, t});
}
if(q.size()) {
int p=q.top().nd, z;
if(p==LIM) z=P.back();
else z=znajdz(0, N-1);
ost=z;
}
}
int main() {
ios_base::sync_with_stdio(0); cin.tie(0);
int n;
cin >> n;
while(N<=n) N*=2;
rep(i, n-1) {
int a, b;
cin >> a >> b; --a; --b;
V[a].pb(b);
V[b].pb(a);
}
int r=0;
rep(i, n) if(V[i].size()>1) r=i;
DFS(r, r);
rep(i, n) if(V[i].size()==1) tr[N+pre[i]]=1;
for(int i=N-1; i; --i) tr[i]=tr[2*i]+tr[2*i+1];
vector<int>P;
DFS2(r, r, P);
if(ost!=-1) T.pb({ost, r});
cout << T.size() << '\n';
for(auto i : T) cout << i.st+1 << " " << i.nd+1 << '\n';
}
