#include<stdio.h>

int main(void){
	double vl,vr,vlp,vrp,d,w,t,r=0;
	scanf("%lf%lf%lf%lf",&vl,&vr,&d,&w);
	vlp=0;vrp=d;
	while(1){
		t = (vrp-vlp)/(vr+w);
		r+=(t*w);
		vlp+=(t*vl);vrp-=(t*vr);
		if(vrp-vlp < 0.0000000001){break;}
		t = (vrp-vlp)/(vl+w);
		r+=(t*w);
		vlp+=(t*vl);vrp-=(t*vr);
		if(vrp-vlp < 0.0000000001){break;}
	}
	printf("%.12lf",r);
	return 0;
}