#include <iostream>
#include <iomanip>
using namespace std;

int main() {
    long double vl, vr, d, w, ans = 0;
    cin >> vl >> vr >> d >> w;
    int i = 0;
    while (d > 0.000001 && i < 100000000) {
        long double t1 = d / (w + vr);
        ans += w * t1;
        d -= (vl + vr) * t1;
        long double t2 = d / (w + vl);
        ans += w * t2;
        d -= (vl + vr) * t2;
        i++;
    }
    
    cout << fixed << setprecision(9) << ans << endl;
    
    return 0;
}