#include <bits/stdc++.h>
using namespace std;
int main() {
  long double d, L, v1, v2, b, c, s, g, p, m;
  cin >> d >> L >> v1 >> v2;
  b = d / 2;
  c = v1 * L;
  s = v2 - v1;
  g = v1 + v2;
  m = (c + (b * s)) / g;
  p = (m - b) / v1;
  cout << setprecision(14) << p << endl;
}
