#include<stdio.h>

int main(){
	double v1,v2,d,w;
	scanf("%lf %lf %lf %lf",&v1,&v2,&d,&w);
	
	double total=0;
	double touch=0;
	int direction=0;
	
	while(d>0.0000001){
		if(direction==0){//右向き
			touch=w*d/(w+v2);//蜂が右の車にぶつかるまでの距離
			total+=touch;
			d-=(v1+v2)*d/(w+v2);//左右の車が動いた距離を減らす
			direction=1;
		}else if(direction==1){//左向き
			touch=w*d/(w+v1);
			total+=touch;
			d-=(v1+v2)*d/(w+v1);
			direction=0;
		}
	}
	
	printf("%f\n",total);
	
	return 0;
}