#include <bits/stdc++.h>
using namespace std;
#pragma comment(linker, "/STACK:167177216")
int main() {
  double y1, y2, yw, xa, ya, r;
  cin >> y1 >> y2 >> yw >> xa >> ya >> r;
  double ll = 0, rr = xa;
  yw -= r;
  double yt = y1 + r + 1e-9;
  for (int i = 0; i < 300; ++i) {
    double xm = (ll + rr) / 2;
    double dx1 = -xm, dy1 = yt - yw;
    double a1 = acos(-dy1 / sqrt(dx1 * dx1 + dy1 * dy1));
    dx1 = xa - xm, dy1 = ya - yw;
    double a2 = acos(-dy1 / sqrt(dx1 * dx1 + dy1 * dy1));
    if (a1 > a2)
      rr = xm;
    else
      ll = xm;
  }
  double xm = (ll + rr) / 2;
  double a = yw - yt, b = -xm, c = -b * yt;
  double d = fabs(b * y2 + c) / sqrt(a * a + b * b);
  if (d + 1e-9 < r) {
    cout << -1 << endl;
    return 0;
  }
  cout.precision(20);
  cout << xm << endl;
  return 0;
}
