#include <bits/stdc++.h>
using namespace std;
int main() {
  long long y1, y2, yw, xb, yb, r;
  cin >> y1 >> y2 >> yw >> xb >> yb >> r;
  long long yd = y1 + r;
  long long h1 = yw - r - yd;
  long long h2 = yw - r - yb;
  long double x = h1 * xb / (long double)(h1 + h2);
  cout.precision(30);
  long double h = sqrt(((x) * (x)) + ((h1) * (h1)));
  long double v = x * (y2 - yd) / h;
  if (r > v - 1e-8)
    printf("-1\n");
  else
    cout << x << endl;
  return 0;
}
