using System;

public class Program
{
    public static void Main()
    {
     int x1 = int.Parse(Console.ReadLine());
    int x2 = int.Parse(Console.ReadLine());
        int y1 = int.Parse(Console.ReadLine());
        int y2 = int.Parse(Console.ReadLine());
        int area = (x2 - x1) * (y1 - y2);
        Console.WriteLine("S = {0}", area);

    }
}