#include <bits/stdc++.h>
using namespace std;
template <class T>
T gcd(T a, T b) {
  return b ? gcd(b, a % b) : a;
}
double sqr(double x) { return x * x; }
int main() {
  double y1, y2, yw, xb, yb, r;
  cin >> y1 >> y2 >> yw >> xb >> yb >> r;
  double ny1 = (yw - r) + (yw - r - y2);
  double ny2 = (yw - r) + (yw - r - (y1 + r));
  double ans = (ny2 - (yw - r)) * xb / (ny2 - yb);
  if (sqr(xb) * sqr(ny1 - ny2) / (sqr(ny2 - yb) + sqr(xb)) < r * r) {
    cout << -1 << endl;
  } else {
    printf("%.10f\n", ans);
  }
}
