#include<stdio.h>

int main(void){
	double a,b,x,y;
	scanf("%lf%lf%lf%lf",&a,&b,&x,&y);
	if(x/a < y/b){printf("%.13lf\n",x*(a+b)/a);}
	else{printf("%.13lf\n",y*(a+b)/b);}
	return 0;
}