#include <bits/stdc++.h>
using namespace std;
int main() {
  double y1, y2, yw, xb, yb, r;
  cin >> y1 >> y2 >> yw >> xb >> yb >> r;
  double yk = yw - r;
  double d1 = yk - (y1 + r);
  double d2 = yk - yb;
  double xk = xb * d1 / (d2 + d1);
  double A = y1 + r - yk;
  double B = xk;
  double C = -B * (y1 + r);
  double h = fabs(B * y2 + C) / sqrt(A * A + B * B);
  double eps = 1e-12;
  if (r > h - eps) {
    cout << -1 << endl;
  } else {
    printf("%.12lf\n", xk);
  }
  return 0;
}
