#include <stdio.h>
int main() {
  float a11, a12, a21, a22, M;
  printf("Unesi brojeve koji ce biti clanovi matrice:\n");
  scanf("%f%f%f%f", &a11, &a12, &a21, &a22);
  M = ((a11 * a22) - (a12 * a21));
  printf("%1.4f\n", M);

  return 0;
}
