#include <bits/stdc++.h>
using namespace std;
const int MAX = 1e5 + 6;
const double eps = 1e-9;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  double y1, y2, yw, xb, yb, r;
  cin >> y1 >> y2 >> yw >> xb >> yb >> r;
  yw -= r;
  yb += 2 * (yw - yb);
  y1 += r;
  double m = (yb - y1) / xb, c = y1;
  double A = m, B = -1.0, C = c;
  double d = abs(B * y2 + C) / sqrt(A * A + B * B);
  if (d <= r) return cout << "-1", 0;
  double x = (yw - c) / m;
  printf("%.10f", x);
}
