#include <bits/stdc++.h>

using namespace std;

double cmmmc(int a, int b){
    int x = a;
    int y = b;
    while(a != b){
        if(a > b)
             b += y;
        else
             a += x;
    }
    return a;
}

int main()
{
    double t1, k1, t2, k2;
    cin>>t1>>k1>>t2>>k2;
    double distanta = cmmmc(t1 , t2);
    double viteza1 = distanta / t1 * k1;
    double viteza2 = distanta / t2 * k2;
    cout<<setprecision(4)<< distanta / (viteza1 + viteza2);
    return 0;
}