#include <bits/stdc++.h>
using namespace std;
int main() {
  double y1, y2, y, xb, yb, r;
  scanf("%lf%lf%lf%lf%lf%lf", &y1, &y2, &y, &xb, &yb, &r);
  y -= r;
  double y0 = y1 + r;
  double x = xb / (1. + (yb - y) / (y0 - y));
  double h = (y2 - y0) * x / sqrt(x * x + (y - y0) * (y - y0));
  if (h < r + 1e-8)
    printf("-1\n");
  else
    printf("%.20lf\n", x);
  return 0;
}
