#include <bits/stdc++.h>
using namespace std;
#define in ({int x=0;int c=getchar(),n=0;for(;!isdigit(c);c=getchar()) n=(c=='-');for(;isdigit(c);c=getchar()) x=x*10+c-'0';n?-x:x;})
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
int rnd(int l,int r){return l+rng()%(r-l+1);}
#define fasty ios_base::sync_with_stdio(0),cin.tie(0);
#define forinc(a,b,c) for(int a=b,_c=c;a<=_c;++a)
#define fordec(a,b,c) for(int a=b,_c=c;a>=_c;--a)
#define forv(a,b) for(auto&a:b)
#define fi first
#define se second
#define pb push_back
#define ii pair<int,int>
#define mt make_tuple
#define all(a) a.begin(),a.end()
#define reset(f, x) memset(f, x, sizeof(f))
#define bit(x,i) ((x>>(i-1))&1)
#define on(x,i) (x|(1ll<<(i-1)))
#define off(x,i) (x&~(1<<(i-1)))
#define gg exit(0);
const int N=100010;
int n;
vector<int> val;
vector<int> ad[N];
void dfs(int u,int p=-1){
if(ad[u].size()<2) val.push_back(u);
forv(v,ad[u]) if(v!=p)
dfs(v,u);
}
main(){
#define task "network"
//freopen(task".inp","r",stdin);
//freopen(task".out","w",stdout);
n=in;
forinc(i,2,n){
int u=in,v=in;
ad[u].pb(v);
ad[v].pb(u);
}
int w=1; while(ad[w].size()<2) w++;
dfs(w);
cout<<(val.size()+1)/2<<"\n";
for(int l=0,r=val.size()-1;l<r;l++,r--)
cout<<val[l]<<" "<<val[r]<<"\n";
if(val.size()&1) cout<<val[val.size()/2]<<" "<<val[0];
}
