func main()
	var n: int :: cui@inputInt()
	var pairs: []Pair :: #[n * (n - 1) / 2]Pair
	var x: []int :: #[n]int
	var y: []int :: #[n]int
	for i(0, n - 1)
		do x[i] :: cui@inputInt()
		do y[i] :: cui@inputInt()
	end for
	
	var idx: int :: 0
	for i(0, n - 1)
		for j(i + 1, n - 1)
			do pairs[idx] :: (#Pair).init(i, j, (x[i] - x[j]) ^ 2 + (y[i] - y[j]) ^ 2)
			do idx :+ 1
		end for
	end for
	do pairs.sort()
	
	var ans: int :: 0
	var used: []bool :: #[n]bool
	for i(0, idx - 1)
		var id1: int :: pairs[i].id1
		var id2: int :: pairs[i].id2
		if(id1 = 0)
			if(!used[id2])
				do used[id2] :: true
				do ans :+ 1
			end if
		else
			if(!used[id1] & !used[id2])
				do used[id1] :: true
				do used[id2] :: true
			end if
		end if
	end for
	do cui@print("\{ans}\n")
	
	class Pair()
		+var id1: int
		+var id2: int
		+var dist: int
		+func init(id1: int, id2: int, dist: int): Pair
			do me.id1 :: id1
			do me.id2 :: id2
			do me.dist :: dist
			ret me
		end func
		+*func cmp(t: kuin@Class): int
			ret me.dist - (t $ Pair).dist
		end func
	end class
end func