#include <bits/stdc++.h>
using namespace std;

#define all(x) begin(x), end(x)
#ifdef CKISEKI
#define safe cerr << __PRETTY_FUNCTION__ << " line " << __LINE__ << " safe\n"
#define debug(a...) debug_(#a, a)
#define orange(a...) orange_(#a, a)
#include <experimental/iterator>
void debug_(auto s, auto ...a) {
  cerr << "\e[1;32m(" << s << ") = (";
  int f = 0;
  (..., (cerr << (f++ ? ", " : "") << a));
  cerr << ")\e[0m\n";
}
void orange_(auto s, auto L, auto R) {
  cerr << "\e[1;33m[ " << s << " ] = [ ";
  using namespace experimental;
  copy(L, R, make_ostream_joiner(cerr, ", "));
  cerr << " ]\e[0m\n";
}
#else
#define safe ((void)0)
#define debug(...) safe
#define orange(...) safe
#endif

using llf = long double;

int main() {
  cin.tie(nullptr)->sync_with_stdio(false);
  int h, r, dx, dy;
  cin >> h >> r >> dx >> dy;

  auto calc = [&](llf y) {
    llf M1 = y * dy; // * pi * r^2
    llf M2 = (h - y) * dx; // * pi * r^2
    llf p1 = y / 2;
    llf p2 = y + (h - y) / 2;
    return (p1 * M1 + p2 * M2) / (M1 + M2);
  };

  llf L = 0, R = h;
  for (int iter = 0; iter < 200; ++iter) {
    llf M1 = L + (R - L) / 3, M2 = R - (R - L) / 3;;
    if (calc(M1) < calc(M2)) R = M2;
    else L = M1; 
  }
  cout << fixed << setprecision(20) << L << '\n';
  return 0;
}