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)
remove = 0

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

puts remove