#include <bits/stdc++.h>
using namespace std;
double cooy1, cooy2, cooyw, cooxb, cooyb, r;
double s1, s2;
int main() {
  ios_base::sync_with_stdio(false);
  cin >> cooy1 >> cooy2 >> cooyw >> cooxb >> cooyb >> r;
  cooy1 += r;
  cooy2 -= r;
  cooyw -= r;
  s1 = 2 * cooyw - cooy1;
  s2 = 2 * cooyw - cooy2;
  double xx1 = cooxb * (cooyw - s1) / (cooyb - s1);
  double xx2 = cooxb * (cooyw - s2) / (cooyb - s2);
  double dd1 = sqrt(cooxb * cooxb + (s1 - cooyb) * (s1 - cooyb)) * r / cooxb;
  double dd2 = sqrt(cooxb * cooxb + (s2 - cooyb) * (s2 - cooyb)) * r / cooxb;
  if (s1 - dd1 < s2 - r) {
    if (s2 - dd2 < s2 - r) {
      cout << -1;
      return 0;
    }
    cout.precision(30);
    cout << xx2;
    return 0;
  } else {
    cout.precision(30);
    cout << xx1;
  }
}
