#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define IOS ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define stdI freopen("input.txt", "r", stdin);
#define stdO freopen("output.txt", "w", stdout);
#define all(x) x.begin(), x.end()
#define mp(x, y) make_pair(x, y)
#define int long long
#define F first
#define S second
using namespace std;
using namespace __gnu_pbds;
typedef tree<int,
null_type,less<int>,
rb_tree_tag,
tree_order_statistics_node_update> ordered_set;
typedef pair<int, int> pii;
const int MAXN = 2e5 + 100, INF = 1e18, MOD = 1e9 + 7;
vector<int> adj[MAXN];
vector<int> b;
int n;
void dfs(int v, int p)
{
if(adj[v].size() == 1)
{
b.push_back(v);
}
for(auto u : adj[v])
{
if(u != p)
{
dfs(u, v);
}
}
}
void solve()
{
cin >> n;
for(int i = 1; i < n; i++)
{
int u, v; cin >> u >> v;
adj[u].push_back(v); adj[v].push_back(u);
}
dfs(1, 0);
if((b.size() & 1))
{
b.push_back(b[0]);
}
int nesf = b.size() / 2;
cout << nesf << "\n";
for(int i = 0; i < nesf; i++)
{
cout << b[i] << " " << b[nesf + i] << "\n";
}
}
int32_t main()
{
IOS;
int t = 1;
//cin >> t;
while(t--)
{
solve();
}
return 0;
}
