#include <bits/stdc++.h>
double Y1, Y2, yw, xb, yb, r;
double Ans, Dist, X, Y, R;
int main() {
  while (~scanf("%lf%lf%lf%lf%lf%lf", &Y1, &Y2, &yw, &xb, &yb, &r)) {
    Ans = xb * (yw - Y1 - 2 * r) / (2 * yw - 3 * r - yb - Y1);
    X = xb - Ans;
    Y = yw - r - yb;
    Dist = sqrt(X * X + Y * Y);
    R = (Y2 - Y1 - r) * X / Dist;
    if (R < r) Ans = -1;
    printf("%.8lf\n", Ans);
  }
  return 0;
}
