#include <stdio.h>

int main ()
{
 float a11, a12, a21, a22; //deklarisanje  elemenata matrice
 float det;
 scanf ("%f%f%f%f", &a11, &a12, &a21, &a22);
 det = (a11*a22)-(a21*a12); // izracunavanje determinante
 printf ("%.4lf\n", det);
return 0;
}

