#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;
	const int sz = 50;
	const int half = 25;
	int loop = 0;
	const long double start_temp = 0,end_temp = 7000;
	auto diff = [&M](long long a,long long b) -> long long
	{
		return max(abs(a - M),abs(b - M));
	};

	auto averaging = [&](long long &a,long long &b) -> void
	{
		long long x = (a + b) / 2;
		a = b = x;
		return;
	};

	auto calc_score = [&](long long a,long long b) -> long double
	{
		return 2e6 - 1e5 * log10(diff(a,b) + 1);
	};

	{
		vector<long long> C = A,D = B;
		for(int i = 2;i <= N;i++)
		{
			ans.push_back(make_pair(1,i));
			averaging(C[0],C[i - 1]);
			averaging(D[0],D[i - 1]);
		}
		score = calc_score(C[0],D[0]);
	}

	while(clock() - start_time < TIME_LIMIT)
	{
		loop++;
		vector<pair<int,int>> n_ans = ans;
		{
			while(true)
			{
				int i = rng() % n_ans.size();
				int j = rng() % n_ans.size();
				if(i == j)
				{
					continue;
				}
				swap(n_ans[i],n_ans[j]);
				break;
			}
		}
		vector<long long> C = A,D = B;
		for(const auto &[u,v] : n_ans)
		{
			averaging(C[u - 1],C[v - 1]);
			averaging(D[u - 1],D[v - 1]);
		}
		long double n_score = calc_score(C[0],D[0]);
		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;
		}
	}


	/* 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; */
	/* } */


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

	//output
	
	cout << ans.size() << "\n";
	for(int i = 0;i < (int)ans.size();i++)
	{
		cout << ans[i].first << " " << ans[i].second << "\n";
	}
	/* cerr << fixed << setprecision(10); */
	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();
}