using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace DanceHall
{
    class Program
    {
        static void Main(string[] args)
        {
            double length = double.Parse(Console.ReadLine());
            double width = double.Parse(Console.ReadLine());
            double side = double.Parse(Console.ReadLine());

            double areaSquareCentimeters = (length * 100) * (width * 100);
            double storage = (side * 100) * (side * 100);
            double bench = areaSquareCentimeters / 10;
            double freeSpace = areaSquareCentimeters - storage - bench;
            double numberOfDancers = Math.Floor(freeSpace / (40 + 7000));

            Console.WriteLine(numberOfDancers);
        }
    }
}