#include <bits/stdc++.h>
using namespace std;
int n, k;
int main() {
  double y1, y2, y, xx, yy, r;
  cin >> y1 >> y2 >> y >> xx >> yy >> r;
  double a = y - y1 - 2 * r, b = y - yy - r, x = a * xx / (a + b),
         l = sqrt(x * x + a * a), ans = x * (y2 - y1 - r) / l;
  if (r - ans > 0)
    cout << "-1" << endl;
  else
    printf("%.10lf", x);
}
