// compile: make data
// run: ./data < data.in > data.out
// run: ./data < data.in
#include <bits/stdc++.h>
using namespace std;
#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
#ifdef LOCAL
#include <debug/codeforces.h>
#define debug(x...) _debug_print(#x, x);
#define Debug(x...) _debug_print_format(#x, x);
std::ifstream terminal("/dev/tty");
#define PP cerr<<"\033[1;30mpause...\e[0m",terminal.ignore();
#else
#define debug(x...)
#define Debug(x...)
#define PP
#endif
template<typename...Args> void print_(Args...args){((cout<<args<<" "),...)<<endl;}
#define rep(i,a,b) for(int i=(a);i<(int)(b);++i)
#define sz(v) ((int)(v).size())
#define print(...) print_(__VA_ARGS__);
#define FIND(a, x) ((find(a.begin(),a.end(),(x))!=a.end())?1:0)
#define cmin(x,...) x=min({(x),__VA_ARGS__})
#define cmax(x,...) x=max({(x),__VA_ARGS__})
#define INTMAX (int)(9223372036854775807)
#define INF (int)(1152921504606846976)
#define NaN (int)(0x8b88e1d0595d51d1)
#define double long double
#define int long long
#define uint unsigned long long
#define MAXN 200010

int32_t main() {
    ios::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr);

    int n; cin >> n;
    vector<vector<int>> e(n);
    rep(i, 0, n-1) {
        int u, v; cin >> u >> v; --u, --v;
        e[u].push_back(v);
        e[v].push_back(u);
    }
    vector<int> leaves;
    function<void(int, int)> dfs = [&](int u, int p) {
        if (sz(e[u]) == 1) leaves.push_back(u);
        for (int v : e[u]) if (v != p) {
            dfs(v, u);
        }
    };
    dfs(0, -1);
    cout << (sz(leaves)+1) / 2 << endl;
    rep(i, 0, (sz(leaves)+1)/2) {
        cout << leaves[i]+1 << ' ' << leaves[i+(sz(leaves)+1)/2]+1 << endl;
    }

    return 0;
}