#include <bits/stdc++.h>
int main() {
  double y1, y2, yw, xb, yb, r;
  double upper;
  double a, b, c, dis;
  while (scanf(" %lf %lf %lf %lf %lf %lf", &y1, &y2, &yw, &xb, &yb, &r) !=
         EOF) {
    yw -= r;
    upper = xb * (yw - y1 - r) / (yw - y1 - r + yw - yb);
    a = yw - yb;
    b = upper - xb;
    c = -(a * upper + b * yw);
    dis = fabs((b * y2 + c) / sqrt(a * a + b * b));
    if (dis - r < 1e-8)
      printf("-1\n");
    else
      printf("%.9lf\n", upper);
  }
  return 0;
}
