package main

import . "fmt"
import "math/rand"

const X=5e17

func abs(a int64) int64 {
	if a<0 {
		return -a
	}
	return a
}

func max(a,b int64) int64 {
	if a<b {
		return b
	}
	return a
}

func main() {
	var n int
	Scan(&n)
	a:=make([]int64,n,n)
	b:=make([]int64,n,n)
	for i:=range a {
		Scan(&a[i],&b[i])
	}
	var u,v []int
	var best int64 = X+X
	
	ta:=make([]int64,n,n)
	tb:=make([]int64,n,n)
	for lp:=0; lp<100000; lp++ {
		copy(ta,a)
		copy(tb,b)
		tu:=make([]int,50,50)
		tv:=make([]int,50,50)
		for i:=0;i<49;i++ {
			p:=rand.Intn(n)
			q:=(p+rand.Intn(n-1)+1)%n
			tu[i],tv[i]=p,q
			aa:=(ta[p]+ta[q])/2
			bb:=(tb[p]+tb[q])/2
			ta[p],tb[p]=aa,bb
			ta[q],tb[q]=aa,bb
		}
		zs:=int64(X+X)
		zi:=-1
		for i:=1;i<n;i++ {
			aa:=(ta[0]+ta[i])/2
			bb:=(tb[0]+tb[i])/2
			s:=max(abs(aa-X),abs(bb-X))
			if s<zs {
				zs,zi=s,i
			}
		}
		if zi>0&&zs<best {
			tu[49],tv[49]=0,zi
			best,u,v=zs,tu,tv
		}
	}
	
	Println(len(u))
	for i,ui:=range u {
		Println(ui+1,v[i]+1)
	}
}