#include <bits/stdc++.h>
using namespace std;
int main() {
  double y1, y2, yw, xb, yb, r;
  cin >> y1 >> y2 >> yw >> xb >> yb >> r;
  if ((r - xb >= 1e-18)) {
    cout << -1;
    return 0;
  }
  double yp = yw - r - (y1 + r);
  double xw = xb * yp / (yw - r - yb + yp);
  if (yp <= 1e-12) {
    cout << -1;
    return 0;
  }
  double dist = xw * (y2 - y1 - r) / sqrt(xw * xw + yp * yp);
  if (dist - r > 1e-18) {
    printf("%0.20f", xw);
  } else
    cout << -1;
}
