#define _USE_MATH_DEFINES
#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#include<bits/stdc++.h>
#include<unordered_map>
#include<random>
#include <array>
#include <complex>
#include<chrono>
using namespace std;
#define LP(I,S,G) for (long long int I = (S); I < (G); ++I)
#define IN(X) 	for (int in = 0; in < X.size(); in++)cin >> X[in]
#define OUT(X) 	for (int in = 0; in < X.size(); in++)cout << X[in]<<" "
#define SORT(X) sort((X).begin(), (X).end())
#define CSORT(X,Y) sort(X.begin(), X.end(),Y)
#define COPY(X,Y) copy(X.begin(), X.end(), Y.begin())
#define ALL(X,Y) for (auto (X) :(Y))
#define FULL(a)  (a).begin(),(a).end()
#define BFS(Q,S) for(Q.push(S);Q.size()!=0;Q.pop())
typedef long long int ll;
typedef unsigned long long int ull;
long long int M = 998244353;

chrono::system_clock::time_point starttime;
using namespace std::chrono;
#ifndef ONLINE_JUDGE
#define DEBUG
#endif

inline float getTime() {
#ifdef DEBUG
	return duration_cast<milliseconds>(system_clock::now() - starttime).count() /4.0;
#else
	return duration_cast<milliseconds>(system_clock::now() - starttime).count();
#endif
}


int dx[] = { -1,0,1,0 }, dy[] = { 0,1,0,-1 };

ll MAX(ll A, ll B) { return ((A) > (B) ? (A) : (B)); }
ll MIN(ll A, ll B) { return ((A) < (B) ? (A) : (B)); }
inline long long int xor128() {
	static long long int x = 123456789, y = 362436069, z = 521288629, w = 88675123;
	long long int t = (x ^ (x << 11));
	x = y; y = z; z = w;
	return (w = (w ^ (w >> 19)) ^ (t ^ (t >> 8)));
}

long long int pow_n(long long int x, long long int n) {
	if (n == 0)
		return 1;
	if (n % 2 == 0)
		return pow_n(x * x, n / 2);
	else
		return x * pow_n(x, n - 1);
}

ll border = 5 * pow_n(10, 17);

double calc_score(array<map<ll, ll>, 45> &ta, array<map<ll, ll>, 45> &tb, vector<pair<ll, ll>>& ans, int from = 0) {
	for (int i = from; i < ans.size(); ++i) {
		int u = ans[i].first, v = ans[i].second;
		ll ua = (--ta[u].upper_bound(i))->second;
		ll va = (--ta[v].upper_bound(i))->second;
		ll ub = (--tb[u].upper_bound(i))->second;
		ll vb = (--tb[v].upper_bound(i))->second;
		ta[u][i + 1] = ta[v][i + 1] = (ua + va) / 2;
		tb[u][i + 1] = tb[v][i + 1] = (ub + vb) / 2;
	}
	return log10(max(abs(border - (--ta[0].upper_bound(50))->second) , abs(border - (--tb[0].upper_bound(50))->second)) + 1);
}

int main(int argc, char* argv[]) {
	starttime = chrono::system_clock::now();
	ios::sync_with_stdio(false);
	std::cin.tie(nullptr);
	mt19937 rnd(0);
	ll n, t = 50, now = 0;
	cin >> n;
	array<map<ll,ll>, 45> ta, tb;
	LP(i, 0, n) {
		ll a, b;
		cin >> a >> b;
		ta[i][0] = a;
		tb[i][0] = b;
	}
	vector<pair<ll, ll>> ans(t);
	LP(i, 0, t) {
		ans[i].first = xor128() % n;
		ans[i].second = xor128() % (n - 1);
		if (ans[i].second >= ans[i].first)++ans[i].second;
	}
	double score = calc_score(ta, tb, ans);
	vector<int> table(t);
	for (int i = 0; i < t; ++i)table[i] = i;
	double time;
	shuffle(table.begin(), table.end(), rnd);
	int cnt = 0;
	while ((time=getTime()) <= 950) {
		double temp = 0.75*(950 - time) / 950.0;
		int i = table[now];
		int bx = ans[i].first, by = ans[i].second;
		ta[bx].erase(i+1);
		ta[by].erase(i+1);
		tb[bx].erase(i+1);
		tb[by].erase(i+1);
		ans[i].first = xor128() % n;
		ans[i].second = xor128() % (n - 1);
		if (ans[i].second >= ans[i].first)++ans[i].second;
		if (xor128() % 10==0) {
			ans[i].first = 0;
			ll minRes = LLONG_MAX;
			ll ua = (--ta[0].upper_bound(i))->second;
			ll ub = (--tb[0].upper_bound(i))->second;
			for (int k = 1; k < n; ++k) {
				ll va = (--ta[k].upper_bound(i))->second;
				ll vb = (--tb[k].upper_bound(i))->second;
				if (max(abs((ua + va) / 2 - border), abs((ub + vb) / 2 - border)) < minRes)minRes = max(abs((ua + va) / 2 - border), abs((ub + vb) / 2 - border)), ans[i].second = k;
			}
		}
		double new_score = calc_score(ta, tb, ans, i);
		if (xor128() % 10000 < exp((score-new_score) / temp) * 10000) {
			score = new_score;
		}
		else {
			ta[ans[i].first].erase(i + 1);
			ta[ans[i].second].erase(i + 1);
			tb[ans[i].first].erase(i + 1);
			tb[ans[i].second].erase(i + 1);
			ans[i].first = bx;
			ans[i].second = by;
			calc_score(ta, tb, ans, i);
		}
		++cnt;
		if (++now == t) {
			now = 0;
			shuffle(table.begin(), table.end(), rnd);
		}
	}
	cerr << cnt;
	cerr << "score:" << ll(2000000 - 100000 * log10(max(abs(border - (--ta[0].upper_bound(50))->second), abs(border - (--tb[0].upper_bound(50))->second)) + 1)) << "\n";
	cerr << (--ta[0].upper_bound(50))->second << " " << (--tb[0].upper_bound(50))->second << "\n";
	cout << ans.size() << "\n";
	ALL(x, ans)cout << x.first+1 << " " << x.second+1 << "\n";
	exit(0);
}