#include <iostream>
#include <vector>
#include <algorithm>

int main(void){
	int t1,k1,t2,k2;
	std::cin>>t1>>k1>>t2>>k2;

	double result = (double)t1/(k1*k2) + (double)t2/(k1*k2) + (double)k1/k2;
	
	std::cout<<result;

	return 0;
}