#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);
  if (y1 > y2) swap(y1, y2);
  y1 += r;
  y2 -= r;
  yw -= r;
  if (y1 > y2 - 1e-8) {
    printf("-1\n");
    return 0;
  }
  double iy = yw + (yw - yb);
  double ix = xb;
  double m = (double)(iy - y1) / (double)(ix - 0);
  double n = y1;
  double res = (yw - n) / m;
  if (abs(y1 - y2 - r) / sqrt(m * m + 1) <= r - 1e-8)
    printf("-1\n");
  else
    printf("%.11lf\n", res);
  return 0;
}
