#include <iostream>
using namespace std;
int main(){
    double A,B,X,Y;
    scanf("%lf %lf %lf %lf",&A,&B,&X,&Y);
    if(X*B<=Y*A)printf("%.7lf\n",X*(1+B/A));
    else printf("%.7lf\n",Y*(1+A/B));
    return 0;
}