#include <bits/stdc++.h>
using namespace std;
int Y1, y2, yw, xb, yb, r;
int main() {
  cin >> Y1 >> y2 >> yw >> xb >> yb >> r;
  if (yb - r < 0) {
    cout << -1 << endl;
    exit(0);
  }
  long double xk = 0, yk = Y1 + r;
  long double xo = (xb * ((yw - r) - yk)) /
                   ((long double)((yw - r) - yk) + ((yw - r) - yb)),
              yo = yw - r;
  long double A = yk - yo;
  long double B = xo - xk;
  long double C = -A * xk - B * yk;
  long double M = sqrt(A * A + B * B);
  A /= M;
  B /= M;
  C /= M;
  cout.precision(15);
  if (fabs(B * y2 + C) >= r) {
    cout << fixed << xo << endl;
  } else {
    cout << -1 << endl;
  }
  return 0;
}
