#include<stdio.h>

int main(void){
	int a,b,x,y;
	scanf("%d%d%d%d",&a,&b,&x,&y);
	double c=(double)a/b;
	double z=(double)x/y;
	if(c<z){
		z=y+c*y;
	} else {
		z=x+x/c;
	}
	printf("%.7lf\n",z);
	return 0;
}