#include <bits/stdc++.h>
using namespace std;
double dis(double x1, double y1, double x2, double y2) {
  return (sqrt((x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1)));
}
int main() {
  double y1, y2, yw, xb, yb, r, ye, yq, k1, b1, nx, ar2;
  cin >> y1 >> y2 >> yw >> xb >> yb >> r;
  ye = y1 + r;
  yq = yw - r;
  ye = yq + (yq - ye);
  k1 = (yb - ye) / xb;
  b1 = ye;
  nx = (yq - b1) / k1;
  ar2 = (y2 - (y1 + r)) * nx;
  if (dis(0, ye, nx, yq) * r > ar2)
    cout << -1 << endl;
  else
    printf("%.10lf\n", nx);
  return 0;
}
