#include <iostream>
#include <vector>
#include <random>

static std::mt19937 mt(0);

using Entry = std::pair<int, int>;

auto gen_random_ans(int n) {
    constexpr int m = 50;
    std::vector<Entry> ans;
    for (int i = 0; i < m; i++) {
        int u, v;
        while (true) {
            u = mt() % n;
            v = mt() % n;
            if (u != v) {
                break;
            }
        }
        ans.emplace_back(u,v);
    }
    return ans;
}

void print_ans(const std::vector<Entry>& ans) {
    std::cout << ans.size() << std::endl;
    for (auto [u,v] : ans) {
        std::cout << u << " " << v << std::endl;
    }
}

int main() {
    int n;
    std::cin >> n;

    std::vector<long> a(n), b(n);
    for (int i = 0; i < n; i++) {
        std::cin >> a[i] >> b[i];
    }

    auto ans = gen_random_ans(n);
    print_ans(ans);
}