#include <iostream>
#include <queue>
using namespace std;
int n;
vector<int> edge[500001];
vector<int> edge_size(500001, 0);
vector<int> p(500001, 0);
vector<int> dfs_leaf;
void dfs(int u)
{
if(edge[u].size() == 1) dfs_leaf.push_back(u);
for(int v: edge[u])
{
if(p[u] == v) continue;
dfs(v);
}
}
int main()
{
cin >> n;
int a, b;
for(int i = 1; i <= n-1; i++)
{
cin >> a >> b;
edge[a].push_back(b);
edge_size[a]++;
edge[b].push_back(a);
edge_size[b]++;
}
queue<int> tbv;
for(int i = 1; i <= n; i++) if(edge_size[i] == 1) tbv.push(i);
while(!tbv.empty())
{
a = tbv.front();
tbv.pop();
for(int v: edge[a])
{
if(p[v] == a) continue;
p[a] = v;
edge_size[v]--;
if(edge_size[v] == 1) tbv.push(v);
}
}
int root = a;
dfs(root);
int s = dfs_leaf.size();
if(s % 2 == 0)
{
cout << s/2 << '\n';
for(int i = 0; i < s/2; i++) cout << dfs_leaf[i] << ' ' << dfs_leaf[s/2 + i] << '\n';
}
else
{
s--;
cout << s/2 + 1 << '\n';
for(int i = 0; i < s/2; i++) cout << dfs_leaf[i] << ' ' << dfs_leaf[s/2 + i] << '\n';
cout << dfs_leaf[0] << ' ' << dfs_leaf[s] << '\n';
}
}
