#include <bits/stdc++.h>
using namespace std;
int main() {
  long double EPS = 1e-10;
  long double y1, y2, yw, xb, yb, r;
  cin >> y1 >> y2 >> yw >> xb >> yb >> r;
  swap(y1, y2);
  yw -= r;
  long double y1m = yw * 2 - y1;
  long double y2m = yw * 2 - y2;
  long double xi = (y2m - y1m - r) / (y2m - yb - r) * xb;
  long double m = -(y2m - yb - r) / xb;
  long double dist = fabs(y1m + m * xb - yb) / sqrt(1 + m * m);
  if (dist <= r + EPS) {
    cout << "-1\n";
    return 0;
  }
  long double ans = (y2m - yw - r) / (y2m - yb - r) * xb;
  cout << fixed << setprecision(10) << ans << "\n";
  return 0;
}
