#include <bits/stdc++.h>
using namespace std;
int main() {
  double y1, y2, yw, xb, yb, r;
  scanf("%lf %lf %lf %lf %lf %lf", &y1, &y2, &yw, &xb, &yb, &r);
  yw -= r;
  y1 = yw * 2 - y1 - r;
  y2 = yw * 2 - y2;
  double l = sqrt(xb * xb + (y1 - yb) * (y1 - yb));
  if (xb * (y1 - y2) / l < r)
    printf("-1\n");
  else
    printf("%.12f\n", xb * (y1 - yw) / (y1 - yb));
  return 0;
}
