#include <bits/stdc++.h>
using namespace std;
using namespace std;
const int mod = (int)1e9 + 7;
const long double INF = (long double)(1e3);
const int N = 100005;
const double PI = acos(-1.0);
const double eps = 1e-9;
int main() {
  double vamdlsfmvldf, y2, yw, xb, yb, r;
  while (cin >> vamdlsfmvldf >> y2 >> yw >> xb >> yb >> r) {
    double yr = yw - r;
    double my1 = yr + (yr - vamdlsfmvldf);
    double my2 = yr + (yr - y2);
    double aim_y = my1 - r;
    double inc_y = (aim_y - yb) / xb;
    double xw = (aim_y - yr) / inc_y;
    double a = PI / 2 - atan2(aim_y - yb, xb);
    double d = r / sin(a);
    if (aim_y - d < my2)
      puts("-1");
    else
      printf("%.10f\n", xw);
  }
}
