#include <stdio.h>
int main(void){
    double A,B,X,Y;
    double c;

    scanf("%lf %lf %lf %lf",&A,&B,&X,&Y);

    //  A:B
    if(X * B / A <= Y){
        c = (double)X * (1 + (double)B / A);
    }else{
        c = (double)Y * (1 + (double)A / B);
    }

    printf("%f\n",c);

    return 0;
}