#include <bits/stdc++.h>
using namespace std;
int main() {
  int y1, y2, yw, xb, yb, r;
  scanf("%d%d%d%d%d%d", &y1, &y2, &yw, &xb, &yb, &r);
  y1 = 2 * (yw - r) - y1;
  y2 = 2 * (yw - r) - y2;
  swap(y1, y2);
  double dx = -xb;
  double dy = y1 - yb;
  double d = sqrt(dx * dx + dy * dy);
  double an = asin(r / d);
  double d1x = dx * cos(an) + dy * sin(an);
  double d1y = -dx * sin(an) + dy * cos(an);
  double t;
  t = (yw - r - yb) / d1y;
  double x1 = xb + t * d1x;
  double d2x = -xb;
  double d2y = (y2 - r - yb);
  t = (yw - r - yb) / d2y;
  double x2 = xb + t * d2x;
  if (x1 >= x2 - 1e-8) {
    printf("-1\n");
    return 0;
  }
  printf("%.17lf\n", (x1 + x2) / 2);
  return 0;
}
