#include<stdio.h>

int main(){
	// 入力された値
	double ratio1 = 0, overall1 = 0;
	scanf("%f%f",&ratio1,&overall1);
	
	double ratio2 = 0,overall2 = 0;
	scanf("%f%f",&ratio2,&overall2);
	
	// 1回に作る分量
	double quantity1 = overall1 / ratio1;
	double quantity2 = overall2 / ratio2;
	
	// 全体製造量
	double ans = 0;
	while(quantity1 < overall1 && quantity2 < overall2){
		overall1 -= quantity1;
		overall2 -= quantity2;
		
		ans += (quantity1 + quantity2);
	}
	printf("%f",&ans);
}