#include <bits/stdc++.h>
using namespace std;
int n, k;
double yx, y2, y, xx, yy, r, a, b, x, l, ans;
int main() {
  cin >> yx >> y2 >> y >> xx >> yy >> r;
  a = y - yx - 2 * r, b = y - yy - r, x = a * xx / (a + b),
  l = sqrt(x * x + a * a), ans = x * (y2 - yx - r) / l;
  if (r - ans > 0)
    cout << "-1" << endl;
  else
    printf("%.10lf", x);
}
