#include <bits/stdc++.h>
template<class T> inline bool chmax(T& a, T b){ if (a < b){ a = b; return true; } return false; }
template<class T> inline bool chmin(T& a, T b){ if (a > b){ a = b; return true; } return false; }
using namespace std;
using ll = long long;
ll mod = 1e9+7;
const int dx[8] = {-1,0,1,0,-1,-1,1,1};
const int dy[8] = {0,1,0,-1,1,-1,1,-1};


int main(){
    double vl, vr, d, w;
    cin >> vl >> vr >> d >> w;
    if (vr > w) {
        printf("%.12f\n", d/(vr+vl));
        return 0;
    }
    if (vl > w) {
        double t1 = d/(vr+w);
        double d1 = d*(1.0-(vl+vr)/(w+vr));
        printf("%.12f\n", t1+d1/(vr+vl));
        return 0;
    }
    double t1 = (1.0/(w+vr) + (1.0-(vl+vr)/(w+vr))/(w+vl) );   //一回の往復に要する見かけ速度の逆数
    double r = (1.0 - (vl+vr)/(vl+w)) * (1.0 - (vl+vr)/(vr+w));
    double ans = w * d * t1 / (1.0-r);
    printf("%.12f\n", ans);
}