#include <bits/stdc++.h>
using namespace std;
const double eps = 1e-8;
int main() {
  int y1, y2, yw, xb, yb, r;
  while (scanf("%d%d%d%d%d%d", &y1, &y2, &yw, &xb, &yb, &r) != EOF) {
    double h1 = yw - (y1 + r) - r;
    double h2 = yw - (yb)-r;
    double ans = h1 * xb / (h1 + h2);
    double a = ((yw - r) - (y1 + r)) / ans;
    double b = -1, c = y1 + r;
    double x = 0, y = y2;
    double dis = fabs(a * x + b * y + c) / sqrt(a * a + b * b);
    if (dis - r < eps) {
      cout << -1 << endl;
      continue;
    }
    printf("%.8lf\n", ans);
  }
  return 0;
}
