#include <bits/stdc++.h>
using namespace std;
const int N = 5e5 + 5; 

int n; 
int a[N], b[N], id[N], c[N], an[N];  

int main(void) {
    ios::sync_with_stdio(0); 
    cin >> n; 
    for (int i = 1; i <= n; ++i) cin >> a[i] >> b[i], id[i] = i; 
    sort(id + 1, id + n + 1, [&](int x, int y) { return b[x] < b[y]; }); 
    int lst = 0, ans = 0; 
    for (int i = 1; i <= n; ++i) {
        
        int x = id[i]; 
        // cout << a[x] << " " << b[x] << "\n"; 
        if (a[x] >= lst) lst = b[x], ++ans, c[x] = 1; 
    }
    // return 0; 
    lst = 0; 
    int cnt = 0, flg = 1, dot = 0; 
    for (int i = 1, r = 0, tmp = 0; i <= n; ++i) {
        int x = id[i]; 
        if (a[x] >= lst) {
            if (tmp && b[tmp] > a[x]) {
                an[x] = tmp; tmp = 0; ++dot; 
                r = lst = b[x]; 
                continue; 
            }
            ++i; 
            while (i <= n) {
                int y = id[i]; 
                if (a[y] < b[x] && a[y] >= r) { an[x] = y; break; } // 不能和真实值相交
                ++i; 
            }
            if (!an[x]) { flg = 0; break; }
            // cerr << a[x] << " " << b[x] << " " << a[an[x]] << " " << b[an[x]] << "\n"; 
            ++dot; 
            lst = b[an[x]]; r = b[x]; 
            // cerr << i << " " << lst << "\n"; 
        } else {
            if (a[x] >= r)
                tmp = x; 
        }
    }
    // return 0; 
    // cerr << dot << "\n"; 
    if (dot == ans) {
        cout << ans << '\n'; 
        for (int i = 1; i <= n; ++i)
            if (an[i]) cout << i << " " << an[i] << "\n"; 
        return 0; 
    }
    cout << ans - 1 << '\n'; 
    vector<int> p; 
    for (int i = 1; i <= n; ++i) if (c[i]) p.push_back(i); 
    for (int i = 0; i < int(p.size() - 1); ++i)
        cout << p[i] << " " << p.back() << "\n"; 
    return 0;
}