#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;
    if (k1 != 0)
        tf1 = t1 / k1;
    else tf1 = t1;
    if(k2 != 0)
        tf2 = t2 / k2;
    else tf2 = t2;

    v1 = d / tf1;
    v2 = d / tf2;

    cout<<d / (v1 + v2);
    return 0;
}