#include <bits/stdc++.h>
int main() {
  double y1, y2, yw, xb, yb, r;
  scanf("%lf %lf %lf %lf %lf %lf", &y1, &y2, &yw, &xb, &yb, &r);
  y1 += r;
  double yx;
  yx = yw - r - yb;
  double xx;
  xx = xb / (1 + yx / (yw - y1 - r));
  double tmp;
  tmp = sqrt((yw - y1 - r) * (yw - y1 - r) + xx * xx);
  double k = xx * ((y2 - y1) / tmp);
  if (k < r)
    printf("-1");
  else
    printf("%.10lf", xx);
  return 0;
}
