#include <bits/stdc++.h>
using namespace std;
int main() {
  int y1, y2, yw, xb, yb, r;
  cin >> y1 >> y2 >> yw >> xb >> yb >> r;
  double EPS = 0;
  double x1 = 1.0 * xb * (yw - (y1 + r + EPS) - r) /
              double(2 * yw - yb - y1 - 3 * r - EPS);
  double sL1 = x1 * x1 + (yw - y1 - 2 * r - EPS) * (yw - y1 - 2 * r - EPS);
  double sd = (y2 - y1 - r - EPS) * (y2 - y1 - r - EPS) * x1 * x1 / sL1;
  if (sd + 1e-8 < double(r) * r)
    cout << -1 << endl;
  else {
    cout.precision(16);
    cout << x1 << endl;
  }
  return 0;
}
