#include <bits/stdc++.h>
int sgn(double x) {
  if (fabs(x) < 1e-12) return 0;
  if (x < 0) return -1;
  return 1;
}
int main() {
  long long y1, y2, yw, xb, yb, r;
  scanf("%I64d%I64d%I64d%I64d%I64d%I64d", &y1, &y2, &yw, &xb, &yb, &r);
  yw -= r;
  double ll = 0, rr = xb;
  for (int i = 0; i < 50; ++i) {
    double mid = (ll + rr) / 2.0;
    double cost =
        (xb - mid) / sqrt((yw - yb) * (yw - yb) + (xb - mid) * (xb - mid));
    double pos = yb + (yw - yb) * (1 - mid / (xb - mid));
    double d = r / cost;
    int ps1 = sgn(pos - r - y1), ps2 = sgn(pos + d - y2);
    if (ps1 > 0 && ps2 < 0) {
      printf("%.12lf\n", mid);
      return 0;
    }
    if (ps1 <= 0 && ps2 >= 0) {
      printf("-1\n");
      return 0;
    }
    if (ps1 > 0)
      ll = mid;
    else
      rr = mid;
  }
  printf("-1\n");
  return 0;
}
