#include <cstdio>
#define repeat(i,n) for (int i = 0; (i) < (n); ++(i))
using namespace std;
int main() {
    int vl, vr, a_d, w; scanf("%d%d%d%d", &vl, &vr, &a_d, &w);
    __float128 d = a_d;
    __float128 acc = 0;
    repeat (i,int(2e6)) {
        __float128 dt = d / (w + vr);
        acc += dt * w;
        d -= dt * (vl + vr);
        dt = d / (vl + w);
        acc += dt * w;
        d -= dt * (vl + vr);
    }
    printf("%.12lf\n", double(acc));
    return 0;
}