#include <iostream>
#include <vector>
#include <algorithm>
#include <array>
#include <iterator>
#include <string>
#include <cctype>
#include <cstring>
#include <cstdlib>
#include <cassert>
#include <cmath>
#include <ctime>
#include <iomanip>
#include <numeric>
#include <stack>
#include <queue>
#include <map>
#include <unordered_map>
#include <set>
#include <unordered_set>
#include <bitset>
#include <random>
#include <utility>
#include <functional>
using namespace std;
void Main()
{
	int start_time = clock();
	//input
	int N;
	cin >> N;
	vector<long long> A(N),B(N);
	for(int i = 0;i < N;i++)
	{
		cin >> A[i] >> B[i];
	}

	const long long M = (long long)5e17;
	const int TIME_LIMIT = 0.9 * CLOCKS_PER_SEC;
	mt19937_64 rng{(unsigned)time(nullptr)};
	vector<pair<int,int>> ans;
	long double score = 0;
	int sz = 50;
	int half = 25;
	int loop = 0;
	long double start_temp = 10,end_temp = 50;

	vector<vector<int>> G(1 << 2);
	vector<int> T(N);
	for(int i = 0;i < N;i++)
	{
		int S = 0;
		if(A[i] > M)
		{
			S |= 1;
		}
		if(B[i] > M)
		{
			S |= 2;
		}
		if(i > 0)
		{
			G[S].push_back(i);
		}
		T[i] = S;
	}

	auto diff = [&M](long long a,long long b) -> long long
	{
		return max(abs(a - M),abs(b - M));
	};

	{
		vector<long long> C = A,D = B;
		for(int i = 0;i < half;i++)
		{
			while(true)
			{
				int u = rng() % (N - 1) + 2;
				/* int v = rng() % (N - 1) + 2; */
				int U = T[u] ^ 3;
				int v = G[U][rng() % G[U].size()] + 1;
				if(u == v)
				{
					continue;
				}
				{
					long long x = (C[u - 1] + C[v - 1]) / 2;
					C[u - 1] = C[v - 1] = x;
				}
				{
					long long x = (D[u - 1] + D[v - 1]) / 2;
					D[u - 1] = D[v - 1] = x;
				}

				ans.push_back(make_pair(u,v));
				break;
			}
		}
		vector<int> ord(N);
		iota(ord.begin(),ord.end(),0);
		sort(ord.begin() + 1,ord.end(),[&](int i,int j)
		{
			return diff(C[i],D[i]) > diff(C[j],D[j]);
		});
		for(int i = N - (sz - half);i < N;i++)
		{
			int id = ord[i];
			{
				long long x = (C[0] + C[id]) / 2;
				C[0] = C[id] = x;
			}
			{
				long long x = (D[0] + D[id]) / 2;
				D[0] = D[id] = x;
			}
			ans.push_back(make_pair(1,id + 1));
		}
		score = 2e6 - 1e5 * log10(diff(C[0],D[0]) + 1);
	}

	while(clock() - start_time < TIME_LIMIT)
	{
		loop++;
		vector<pair<int,int>> n_ans(ans.begin(),ans.begin() + half);
		{
			int id = rng() % half;
			while(true)
			{
				int u = rng() % (N - 1) + 2;
				/* int v = rng() % (N - 1) + 2; */
				int U = T[u] ^ 3;
				int v = G[U][rng() % G[U].size()] + 1;
				if(u == v)
				{
					continue;
				}
				n_ans[id] = make_pair(u,v);
				break;
			}
		}
		long double n_score = 0;
		vector<long long> C = A,D = B;
		for(const auto &[u,v] : n_ans)
		{
			{
				long long x = (C[u - 1] + C[v - 1]) / 2;
				C[u - 1] = C[v - 1] = x;
			}
			{
				long long x = (D[u - 1] + D[v - 1]) / 2;
				D[u - 1] = D[v - 1] = x;
			}
		}
		vector<int> ord(N);
		iota(ord.begin(),ord.end(),0);
		sort(ord.begin() + 1,ord.end(),[&](int i,int j)
		{
			return diff(C[i],D[i]) > diff(C[j],D[j]);
		});
		for(int i = N - (sz - half);i < N;i++)
		{
			int id = ord[i];
			{
				long long x = (C[0] + C[id]) / 2;
				C[0] = C[id] = x;
			}
			{
				long long x = (D[0] + D[id]) / 2;
				D[0] = D[id] = x;
			}
			n_ans.push_back(make_pair(1,id + 1));
		}
		n_score = 2e6 - 1e5 * log10(diff(C[0],D[0]) + 1);
		long double temp = start_temp + (end_temp - start_temp) * (clock() - start_time) / TIME_LIMIT;
		long double prob = exp((n_score - score) / temp);
		if(prob >= (long double)(rng() % M) / M)
		{
			swap(ans,n_ans);
			score = n_score;
		}
		/* if(n_score > score) */
		/* { */
		/* 	swap(ans,n_ans); */
		/* 	score = n_score; */
		/* } */
	}

	//output
	cout << ans.size() << "\n";
	for(int i = 0;i < (int)ans.size();i++)
	{
		cout << ans[i].first << " " << ans[i].second << "\n";
	}
	cerr << "Score : " << score << "\n";
	cerr << "Loop : " << loop << "\n";
}
int main()
{
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int tt = 1;
	/* cin >> tt; */
	while(tt--) Main();
}