#include <stdio.h>
int main()
{
int A, B, C, D;
scanf("%d %d %d %d", &A
, &B
, &C
, &D
);
long long result = (A * B) - (C * D);
printf("Difference = %lld\n", result
);
return 0;
}
I2luY2x1ZGUgPHN0ZGlvLmg+CgppbnQgbWFpbigpCnsKCWludCBBLCBCLCBDLCBEOwoKCXNjYW5mKCIlZCAlZCAlZCAlZCIsICZBLCAmQiwgJkMsICZEKTsKCglsb25nIGxvbmcgcmVzdWx0ID0gKEEgKiBCKSAtIChDICogRCk7CgoJcHJpbnRmKCJEaWZmZXJlbmNlID0gJWxsZFxuIiwgcmVzdWx0KTsKCglyZXR1cm4gMDsKfQo=