#include <bits/stdc++.h>
using namespace std;
#define int long long
#define pb push_back
#define mp make_pair
#define pii pair<int,int>
#define ss second
#define ff first
#define piii pair<int,pii>
#define debu(x) (cerr << #x << " = "<< x << "\n")
#define debu2(x,y) (cerr << #x << " = "<< x << " " << #y << " = " << y << "\n")
#define debu3(x,y,z) (cerr << #x << " = "<< x << " " << #y << " = " << y << " " << #z << " = " << z<< "\n")
#define bitout(x,y) {\
cerr << #x << " : ";\
for (int justforbits = y; justforbits >=0; justforbits--)cout << (((1 << justforbits) & x)>=1);\
cout << "\n";\
}
#define rangeout(j,rangestart,rangeend) {\
cerr << "outputting" << #j<< ":\n";\
for (int forrang = rangestart; forrang <= rangeend; forrang++)cerr << j[forrang] << " ";\
cerr<<"\n";\
}
#define c1 {cerr << "Checkpoint 1! \n\n";cerr.flush();}
#define c2 {cerr << "Checkpoint 2! \n\n";cerr.flush();}
#define c3 {cerr << "Checkpoint 3! \n\n";cerr.flush();}
#define c4 {cerr << "Checkpoint 4! \n\n";cerr.flush();}
#define defN 500001
vector<vector<int>>adjlist(defN);
vector<int>preorder(defN);
int curr=0;
void dfs(int cn)
{
preorder[cn]=++curr;
for(int to:adjlist[cn])
{
if(preorder[to])continue;
dfs(to);
}
}
signed main()
{
int t1,t2,t3,t4;
mt19937_64 rnd(chrono::high_resolution_clock::now().time_since_epoch().count());
//ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
int n;cin>>n;
for(int a=1;a<n;a++)
{
cin>>t1>>t2;
adjlist[t2].pb(t1);
adjlist[t1].pb(t2);
}
int myroot;
for(int a=1;a<=n;a++)
{
if(adjlist[a].size()!=1)
{
myroot=a;break;
}
}
dfs(1);
vector<pii>myliz;
for(int a=1;a<=n;a++)
{
if(adjlist[a].size()==1)
{
myliz.pb(mp(preorder[a],a));
}
}
sort(myliz.begin(),myliz.end());
cout<<myliz.size()/2+myliz.size()%2<<"\n";
for(int a=0;a<myliz.size()/2;a++)
{
cout<<myliz[a].ss<<" "<<myliz[a+myliz.size()/2].ss<<"\n";
}
if(myliz.size()%2)cout<<myliz[myliz.size()/2].ss<<" "<<myliz[myliz.size()-1].ss<<"\n";
}
