#include <bits/stdc++.h> using namespace std; ifstream fin ("data.in"); long double t1,t2,k1,k2; long double tf1, tf2 , v1, v2; long double d = 10000000; int main() { cin>>t1>>k1>>t2>>k2; tf1 = t1 / k1; tf2 = t2 / k2; v1 = d / tf1; v2 = d / tf2; cout<<d / (v1 + v2); return 0; }