#include<iostream>
#include<fstream>

int main()
{
	int t1, t2, k1, k2;
	int distance = 418;
	std::ifstream file;
	file.open("in.txt");
	file >> t1;
	file >> k1;
	file >> t2;
	file >> k2;
	file.close();
	int v1, v2;
	v1 = distance / t1;
	v2 = distance / t2;
	float result=(float)distance/(v1*k1 + v2*k2);
	std::ofstream outfile;
	outfile.open("out.txt");
	outfile << result;
	outfile.close();
	return 0;
}