n = gets.to_i
xy = []
n.times {
	xy << gets.split(" ").map{|s| s.to_i}
}

dist = []

0.upto(n-1) {|i|
	xi, yi = xy[i]
	(i+1).upto(n-1) {|j|
		xj, yj = xy[j]
		d = (xi-xj)**2 + (yi-yj)**2
		dist << [d, i, j]
	}
}

dist.sort!

alive = Array.new(n, 1)
alive_n = n
remove = 0

while alive_n > 1
	d, i, j = dist.shift
	if i == 0 and alive[j] == 1 then
		remove += 1
		alive[j] = 0
		alive_n -= 1
	elsif alive[i] == 1 and alive[j] == 1 then
		alive[i] = alive[j] = 0
		alive_n -= 2
	end
end