#include<bits/stdc++.h>
using namespace std;
#define int long long
#define F first
#define S second
#define pii pair<int,int>
#define mpr make_pair
typedef long long ll;
//typedef long double ld;
const int maxn = 5e5+10;
const int mod = 1e9+7;
const int inf = (1ll<<40)-1;
int n, m, k;
int st[maxn], par[maxn], tin[maxn], tim, cent;
vector<int> ve, g[maxn];
int num_of_leaf;
void dfs(int v)
{
if(g[v].size() == 1)
{
ve.push_back(v);
tin[v] = tim++;
}
int mx = 0;
if(g[v].size() == 1) st[v] = 1;
else st[v] = 0;
for(auto u : g[v])
if(u != par[v])
{
par[u] = v;
dfs(u);
mx = max(mx,st[u]);
st[v] += st[u];
}
mx = max(mx, num_of_leaf-st[v]);
if(mx <= num_of_leaf/2) cent = v;
}
signed main()
{
//ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
cin>> n;
for(int i = 1, u, v; i < n; i++)
{
cin>> u >> v;
g[u].push_back(v);
g[v].push_back(u);
}
for(int v = 1; v <= n; v++) if(g[v].size() == 1) num_of_leaf++;
dfs(1);
ve.clear();
tim = 0;
par[cent] = 0;
dfs(cent);
int m = num_of_leaf; /// = ve.size()
if(m%2 == 0)
{
cout<< m/2 <<"\n";
for(int i = 0; i < m/2; i++)
cout<< ve[i] <<" "<< ve[i+m/2] <<"\n";
}
else
{
cout<< (m+1)/2 <<"\n";
for(int i = 0; i < (m+1)/2; i++)
cout<< ve[i] <<" "<< ve[i+m/2] <<"\n";
}
}
/*
8
1 2
2 3
3 4
4 5
3 6
3 7
3 8
*/
