#include <bits/stdc++.h>
using namespace std;
template <typename T>
T next() {
  T a;
  cin >> a;
  return a;
}
int main() {
  double y1 = next<int>();
  double y2 = next<int>();
  double yw = next<int>();
  double xb = next<int>();
  double yb = next<int>();
  double r = next<int>();
  double hh = yw - y1 - 2.0 * r;
  double aa = (xb * hh) / (hh + yw - yb - r);
  double sinalpha = aa / (sqrt(aa * aa + hh * hh));
  double d = r + r / sinalpha;
  if (y2 - y1 - d < -DBL_EPSILON)
    cout << -1 << endl;
  else
    printf("%0.9lf\n", aa);
  return 0;
}
