#include <bits/stdc++.h>
using namespace std;
int main() {
  cout.setf(ios::fixed);
  cout.precision(12);
  double y1, y2, yw, xb, yb, r;
  cin >> y1 >> y2 >> yw >> xb >> yb >> r;
  double yn = yw - r + (yw - r - yb);
  double yg = y1 + r;
  double a = (yn - yg) / xb;
  double b = yg;
  double d = fabs(-y2 + b) / sqrt(a * a + 1);
  if (d < r - 0.0000000001)
    cout << -1 << endl;
  else
    cout << (yw - r - b) / a << endl;
}
