#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 vit1 = dist/t1*k1;
    float vit2 = dist/t2*k2;
    cout<<setprecision(4)<<dist/(vit1+vit2);
    return 0;
}