#include <bits/stdc++.h>

using i64 = long long;
using u64 = unsigned long long;
using u32 = unsigned;
using u128 = unsigned __int128;

int main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    
    int n;
    std::cin >> n;
    
    std::vector<std::array<int, 3>> a(n);
    for (int i = 0; i < n; i++) {
        int l, r;
        std::cin >> l >> r;
        a[i] = {r, l, i};
    }
    std::sort(a.begin(), a.end());
    
    int R = 0;
    std::vector<int> ans;
    for (auto [r, l, i] : a) {
        if (l >= R) {
            ans.push_back(i);
            R = r;
        }
    }
    
    std::cout << ans.size() - 1 << "\n";
    for (int i = 1; i < ans.size(); i++) {
        std::cout << ans[i] + 1 << " " << ans[0] + 1 << "\n";
    }
    
    return 0;
}