1007.java

import java.io.IOException;
import java.util.Scanner;

public class Main {
 
    public static void main(String[] args) throws IOException {
 
        int A, B, C, D, diferenca;
        Scanner sc = new Scanner(System.in);
        
        A = sc.nextInt();
        B = sc.nextInt();
        C = sc.nextInt();
        D = sc.nextInt();
        diferenca = (A*B - C*D);
        
        System.out.printf("DIFERENCA = %d\n", diferenca);
    }
 
}