#include <bits/stdc++.h>
#define foreach for
#define in :
using namespace std;
typedef long long ll;
/*
Konichiwa
Konichiwa
Ara ~~ ara
Bob no taisuki - Shinobu Kocho
* * * * *
* *
* *
* * I love SHINOBU <3 <3 <3
* *
* *
* * * * *
*/
/*
_________________________
Author : Bob15324
_________________________
*/
template<class X , class Y>
bool Minimize(X & x , Y y)
{
if(x == -1 || x >y)
{
x = y;
return true;
}
return false;
}
template<class X , class Y>
bool Maximize(X & x , Y y)
{
if( x < y)
{
x = y;
return true;
}
return false;
}
/* End of templates. Let's see what do we have here */
const int N = 5e5+1;
int n , deg[N] ;
vector<int>Leaves;
class GRAPH
{
private:
vector<vector<int>>vertices;
public :
GRAPH(int _n)
{
vertices.resize(_n+1);
}
void AddEdge(int u ,int v)
{
vertices[u].push_back(v);
vertices[v].push_back(u);
}
void DFS(int u ,int daddy)
{
if(deg[u] == 1)
{
Leaves.push_back(u);
}
foreach(int v in vertices[u])
{
if(v == daddy)
{
continue;
}
DFS(v , u);
}
}
};
int u ,v;
int main()
{
ios_base :: sync_with_stdio(0);cin.tie(0);
cin >> n;
GRAPH graph(n);
for(int i = 1; i <= n-1 ; i++)
{
cin >> u >> v;
graph.AddEdge(u , v);
deg[u]++;
deg[v]++;
}
graph.DFS(1 , -1);
cout << (((int)Leaves.size() + 1) >> 1) <<'\n' ;
for(int i = 0 ; i <= ((int)Leaves.size() >> 1) - 1 ; i++)
{
cout << Leaves[i] << ' ' << Leaves[i + ((int)Leaves.size() >> 1 )] <<'\n';
}
if(((int)Leaves.size() ) & 1)
{
cout << (int)Leaves[(int)Leaves.size()-1] << ' ' << (int)Leaves[((int)Leaves.size()) >> 1] <<'\n';
}
return 0;
}
