from math import floor

length = float(input())
width = float(input())
side_of_wardrobe = int(input())

area_of_hall = length * width * 10000
area_of_wardrobe = side_of_wardrobe * side_of_wardrobe * 10000

bench = area_of_hall / 10

free_space = area_of_hall - area_of_wardrobe - area_of_bench

dancers = free_space / 7040

print(floor(dancers))