#include <bits/stdc++.h>
using namespace std;
template <typename T, typename U>
inline void smin(T &a, U b) {
  if (a > b) a = b;
}
template <typename T, typename U>
inline void smax(T &a, U b) {
  if (a < b) a = b;
}
struct point {
  long double first, second;
  point(long double first = 0, long double second = 0)
      : first(first), second(second) {}
  point operator-(point a) { return point(first - a.first, second - a.second); }
  point operator+(point a) { return point(first + a.first, second + a.second); }
  point operator*(long double a) { return point(first * a, second * a); }
  point operator/(long double a) { return point(first / a, second / a); }
  point operator&(point a) {
    return point(first * a.first - second * a.second,
                 first * a.second + second * a.first);
  }
  long double operator^(point a) { return first * a.second - second * a.first; }
  long double operator*(point a) { return first * a.first + second * a.second; }
  point norm() {
    long double s = nor();
    if (s < 1e-8) return *this;
    return point(first / s, second / s);
  }
  long double nor() { return sqrt(*this * *this); }
  long double al() { return atan2l(second, first); }
  bool operator<(const point &a) const {
    if (fabs(first - a.first) > 1e-8) return first < a.first;
    return second < a.second - 1e-8;
  }
  bool operator>(const point &a) const {
    if (fabs(first - a.first) > 1e-8) return first > a.first;
    return second > a.second + 1e-8;
  }
  bool operator==(const point &a) const {
    if (fabs(first - a.first) > 1e-8) return 0;
    return fabs(second - a.second) < 1e-8;
  }
};
point intersect(point a, point b, point c, point d) {
  long double s1 = fabsl((a - b) ^ (c - b)), s2 = fabsl((a - b) ^ (d - b));
  return (c * s2 + d * s1) / (s1 + s2);
}
long double dist(point a, point b, point c) {
  return fabs((a - b) ^ (b - c)) / (a - b).nor();
}
int main() {
  long double y1, y2, yw, xb, yb, r;
  cin >> y1 >> y2 >> yw >> xb >> yb >> r;
  y1 += r, y2 -= r, yw -= r;
  y1 = yw * 2 - y1, y2 = yw * 2 - y2;
  swap(y1, y2);
  y1 -= r;
  if (dist(point(xb, yb), point(0, y2 - 1e-8), point(0, y1)) < r + 1e-8)
    puts("-1");
  else
    printf("%.18lf\n", (double)intersect(point(xb, yb), point(0, y2 - 1e-8),
                                         point(0, yw), point(xb, yw))
                           .first);
  return 0;
}
