#include <bits/stdc++.h>
using namespace std;
#define rep(i,a,n) for (int i=a;i<n;i++)
#define per(i,a,n) for (int i=n-1;i>=a;i--)
#define pb push_back
#define mp make_pair
#define all(x) (x).begin(),(x).end()
#define fi first
#define se second
#define SZ(x) ((int)(x).size())
typedef vector<int> VI;
typedef long long ll;
typedef pair<int,int> PII;
typedef double db;
mt19937 mrand(random_device{}());
const ll mod=1000000007;
int rnd(int x) { return mrand() % x;}
ll powmod(ll a,ll b) {ll res=1;a%=mod; assert(b>=0); for(;b;b>>=1){if(b&1)res=res*a%mod;a=a*a%mod;}return res;}
ll gcd(ll a,ll b) { return b?gcd(b,a%b):a;}
// head
const int N=101000;
int n;
VI g[N],l;
void dfs(int x,int f) {
bool lf=true;
for (auto u:g[x]) {
if (u!=f) {
dfs(u,x);
lf=false;
}
}
if (lf) l.pb(x);
}
int main() {
scanf("%d",&n);
rep(i,1,n) {
int x,y;
scanf("%d%d",&x,&y);
g[x].pb(y);
g[y].pb(x);
}
int rt=-1;
rep(i,1,n+1) if (SZ(g[i])>1) rt=i;
assert(rt!=-1);
dfs(rt,0);
vector<PII> ans;
for (int i=0;i<SZ(l)/2;i++) {
ans.pb(mp(l[i],l[SZ(l)-i-1]));
}
if (SZ(l)&1) ans.pb(mp(l[SZ(l)/2],l.back()));
printf("%d\n",SZ(ans));
rep(i,0,SZ(ans)) printf("%d %d\n",ans[i].fi,ans[i].se);
// if (SZ(l)%2==1&&SZ(l)>1) printf("%d %d\n",l[SZ(l)-2],l[SZ(l)-1]);
}
