#include <bits/stdc++.h>
using namespace std;
const double pi = acos(-1.0);
const double eps = 1e-8;
const double seps = 1e-6;
void finish_bad() {
  cout << -1 << endl;
  exit(0);
}
void finish_ok(double x) {
  cout.precision(20);
  cout << x << endl;
  exit(0);
}
int main() {
  double y1, y2, yw, xb, yb, r;
  cin >> y1 >> y2 >> yw >> xb >> yb >> r;
  if (xb < r + eps) finish_bad();
  double ytp = y1 + r + seps;
  double h = (yw - r - yb) / (yw - r - ytp) + 1;
  double xans = xb / h;
  double vx = -(yw - ytp - r), vy = xans;
  double k = sqrt(vx * vx + vy * vy);
  vx /= k;
  vy /= k;
  if (vy * (y2 - ytp) < r + eps) finish_bad();
  finish_ok(xans);
  return 0;
}
