#include <bits/stdc++.h>
using namespace std;
int main() {
  int y1, y2, yw, xb, yb, r;
  cin >> y1 >> y2 >> yw >> xb >> yb >> r;
  double a, b, c, newy1, newy2;
  newy2 = 2 * (yw - r) - y2;
  newy1 = 2 * (yw - r) - y1;
  double eps = 0.000001;
  double newy = newy1 - r;
  a = newy - yb;
  b = xb;
  c = -a * xb - b * yb;
  double x = (-b * (yw - r) - c) / a;
  double r2 = (fabs(b * newy2 + c)) / sqrt(a * a + b * b);
  if (r2 < r + eps) {
    cout << -1;
    return 0;
  }
  cout.precision(10);
  cout << fixed << x;
  cin >> x;
  return 0;
}
