#include <bits/stdc++.h>
using namespace std;
int main() {
  double y1, y2, yw, xb, yb, r;
  while (~scanf("%lf%lf%lf%lf%lf%lf", &y1, &y2, &yw, &xb, &yb, &r)) {
    int flag = 0;
    double x = (xb * yw - xb * r - xb * (y1 + r) * 1.0) /
               (yw - 2 * r - yb - (y1 + r) * 1.0 + yw);
    double xxx = r / sin(atan(x / (yw - r - (y1 + r))));
    if (y1 + r + xxx < y2) {
      printf("%.10f\n", x);
      flag = 1;
    }
    if (!flag) {
      printf("-1\n");
    }
  }
  return 0;
}
