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

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

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

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

    return 0;
}