#include <bits/stdc++.h>
using namespace std;
const int eps = 1e-10, maxn = 100;
const double pi = acos(-1);
struct Point {
  double x, y;
  Point(double x = 0, double y = 0) : x(x), y(y) {}
};
Point operator+(Point A, Point B) { return Point(A.x + B.x, A.y + B.y); }
Point operator-(Point A, Point B) { return Point(A.x - B.x, A.y - B.y); }
Point operator*(Point A, double p) { return Point(A.x * p, A.y * p); }
Point operator/(Point A, double p) { return Point(A.x / p, A.y / p); }
int dcmp(double x) {
  if (fabs(x) < eps)
    return 0;
  else
    return x < 0 ? -1 : 1;
}
bool operator==(Point A, Point B) {
  return dcmp(A.x - B.x) == 0 && dcmp(A.y - B.y) == 0;
}
bool operator<(Point A, Point B) {
  return dcmp(A.x - B.x) < 0 || dcmp(A.x - B.x) == 0 && dcmp(A.y - B.y) < 0;
}
double Dot(Point A, Point B) { return A.x * B.x + A.y * B.y; }
double Cross(Point A, Point B) { return A.x * B.y - A.y * B.x; }
double Length(Point A) { return sqrt(Dot(A, A)); }
Point GetLineIntersection(Point P, Point v, Point Q, Point w) {
  return P + v * Cross(w, P - Q) / Cross(v, w);
}
int main() {
  double y1, y2, yw, xb, yb, r;
  scanf("%lf%lf%lf%lf%lf%lf", &y1, &y2, &yw, &xb, &yb, &r);
  Point A, B;
  A = {xb, 2 * yw - 2 * r - yb};
  B = {0, y1 + r};
  double h = r * Length(A - B) / xb;
  if (y1 + r + h > y2)
    printf("-1\n");
  else {
    Point C = GetLineIntersection(A, A - B, {0, yw - r}, {1, 0});
    printf("%.10lf\n", C.x);
  }
  return 0;
}
