#include <bits/stdc++.h>

using namespace std;

float 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()
{
    float t1,k1,t2,k2;
    cin >> t1 >> k1 >> t2 >> k2;
         float dist=cmmmc(t1,t2);
               float v1=dist/t1*k1;
    float v2 = dist/t2*k2;
    cout << setprecision(4) << dist/(v1+v2);
        return 0;
}