using System;

public class Hello
{
    public static void Main()
    {
        string[] line = Console.ReadLine().Trim().Split(' ');
        var a = long.Parse(line[0]);
        var b = long.Parse(line[1]);
        var c = long.Parse(line[2]);
        var x = c * c - b * c + b * b - a * c;
        Console.WriteLine(x / (b - a));
    }
}