#include <bits/stdc++.h>
#pragma warning(disable : 4244 4267 4018 4996 4800)
using namespace std;
istream& in = cin;
ostream& out = cout;
int main() {
  double y1, y2, yw, xb, yb, r;
  in >> y1 >> y2 >> yw >> xb >> yb >> r;
  double xw = xb * (yw - r - y1 - r) / (yw - r - yb + yw - r - y1 - r);
  double y = y1 + r;
  double a = y - yw + r, b = xw;
  double d = sqrt(a * a + b * b);
  a /= d;
  b /= d;
  double c = -b * y;
  double dist = abs(b * y2 + c);
  if (dist < r - 1e-9) {
    out << -1;
    return 0;
  }
  out.setf(ios::fixed);
  out.precision(10);
  out << xw;
  return 0;
}
