#include <bits/stdc++.h>
using namespace std;
int main(int argc, char *argv[]) {
  double y1, y2, yw, xb, yb, r;
  cin >> y1 >> y2 >> yw >> xb >> yb >> r;
  double x = xb * (yw - 2 * r - y1) / (2 * yw - 3 * r - yb - y1);
  cout.precision(12);
  if ((y2 - y1 - r) * sin(atan(x / (yw - 2 * r - y1))) > r)
    cout << fixed << x << endl;
  else
    cout << -1 << endl;
  return 0;
}
