#include <bits/stdc++.h>
#pragma comment(linker, "/STACK:256000000")
using namespace std;
const double eps = 1e-9;
double get(double a, double b, double d) { return a * d / (a + b); }
int main() {
  double y1, y2, yw, xb, yb, r;
  cin >> y1 >> y2 >> yw >> xb >> yb >> r;
  yw -= r;
  y1 += r, y2 -= r;
  if (y1 > y2 + eps) {
    cout << "-1" << endl;
    return 0;
  }
  y2 += r;
  double xr = get(yw - y1, yw - yb, xb);
  double d = fabs(y2 * xr - xr * y1) / sqrt((y1 - yw) * (y1 - yw) + xr * xr);
  if (d < r - eps) {
    cout << "-1" << endl;
    return 0;
  }
  printf("%.10lf\n", xr);
  return 0;
}
