#include <bits/stdc++.h>
using namespace std;
int main() {
  double y1, y2, yw, xb, yb, r;
  cin >> y1 >> y2 >> yw >> xb >> yb >> r;
  yw -= r;
  yb = (yw * 2) - yb;
  double b = -2 * (yb - y2);
  double a = xb * xb / r / r - 1;
  double c = -xb * xb - (yb - y2) * (yb - y2);
  double b2_4ac = b * b - 4 * a * c;
  double sqrtb2_4ac = sqrt(b2_4ac);
  double tempy2 = (-b + sqrtb2_4ac) / 2 / a;
  tempy2 = y2 - tempy2;
  double tempy1 = y1 + r;
  if (tempy1 >= tempy2) {
    cout << "-1" << endl;
  } else {
    double tempy = (tempy1 + tempy2) / 2;
    double xw = xb * (yw - tempy) / (yb - tempy);
    printf("%.9lf\n", xw);
  }
  return 0;
}
