#include <bits/stdc++.h>
using namespace std;

long long N;
long long A[59];
long long B[59];

const long long avg = 500000000000000000;

int main() {
	// Step 1. 入力
	cin >> N;
	for (int i = 1; i <= N; i++) cin >> A[i] >> B[i];

	// Step 2. 出力
    vector<pair<int,int>> output;
	for (int i = 1; i <= 50; i++) {
		long long A_max=0;
		int A_max_itr;
		long long B_max=0;
		int B_max_itr;

		long long A_min=5000000000000000000;
		int A_min_itr;
		long long B_min=5000000000000000000;
		int B_min_itr;

        for (int j = 1; j <= N; j++){
            if( A[j]>A_max ){
                A_max_itr = j;
                A_max = A[j];
            }
            if( B[j]>B_max ){
                B_max_itr = j;
                B_max = A[j];
            }
            if( A[j]<A_min ){
                A_min_itr = j;
                A_min = A[j];
            }
            if( B[j]<B_min ){
                B_min_itr = j;
                B_min = A[j];
            }
        }

        /*
        cout << "A_max_itr" << " " << A_max_itr << "," << A_max << endl;
        cout << "A_min_itr" << " " << A_min_itr << "," << A_min << endl;
        cout << "B_max_itr" << " " << B_max_itr << "," << B_max << endl;
        cout << "B_min_itr" << " " << B_min_itr << "," << B_min << endl;
        */

        long long A_avg = (A_max+A_min)/2;
        long long B_avg = (B_max+B_min)/2;
        if( abs(A_avg-avg)>abs(B_avg-avg) ){
            if(A_max_itr!=A_min_itr){
                A[A_max_itr] = A_avg;
                A[A_min_itr] = A_avg;
                long long B_avg_2 = (B[A_max_itr]+B[A_min_itr])/2;
                B[A_max_itr] = B_avg_2;
                B[A_min_itr] = B_avg_2;
                //cout << A_max_itr << " " << A_min_itr << endl;
                output.push_back({A_max_itr,A_min_itr});
            }
        }
        else{
            if(B_max_itr!=B_min_itr){
                B[B_max_itr] = B_avg;
                B[B_min_itr] = B_avg;
                long long A_avg_2 = (A[B_max_itr]+A[B_min_itr])/2;
                A[B_max_itr] = A_avg_2;
                A[B_min_itr] = A_avg_2;
                //cout << B_max_itr << " " << B_min_itr << endl;
                output.push_back({B_max_itr,B_min_itr});
            }
        }
	}

    
	cout << output.size() << endl;
    for(auto x:output){
        cout << x.first << " " << x.second << endl;
    }
	return 0;
}