#define _USE_MATH_DEFINES
#include <cstdio>
#include <iostream>
#include <sstream>
#include <fstream>
#include <iomanip>
#include <algorithm>
#include <cmath>
#include <complex>
#include <string>
#include <vector>
#include <list>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <bitset>
#include <numeric>
#include <limits>
#include <climits>
#include <cfloat>
#include <functional>
#include <iterator>
using namespace std;

int main()
{
    double v1, v2, d, w;
    cin >> v1 >> v2 >> d >> w;
    v1 /= w;
    v2 /= w;

    double t = (2.0 * d) / ((v1 + 1) * (v2 + 1));
    double d2 = d - (v1 + v2) * t;

    double r = d2 / d;
    double ans = t / (1.0 - r);
    printf("%.10f\n", ans);

    return 0;
}