#include <bits/stdc++.h>
using namespace std;
void debugarr(int* arr, int n) {
  cout << "[ ";
  for (int i = 0; i < n; i++) cout << arr[i] << " ";
  cout << "]" << endl;
}
int main() {
  int y1, y2, yw, xb, yb, r;
  cin >> y1 >> y2 >> yw >> xb >> yb >> r;
  double ans = (double)xb * (yw - y1 - 2 * r);
  ans = ans / (double)(2 * yw - y1 - 3 * r - yb);
  double m = (double)(2 * yw - y1 - 3 * r - yb);
  m /= (double)xb;
  double n = 1 + m * m;
  n = sqrt(n);
  if (y2 <= y1 + r + r * n) {
    cout << -1 << endl;
  } else {
    cout.precision(15);
    ans = ans - 1e-12;
    cout << ans << endl;
  }
}
