#include <bits/stdc++.h>
using namespace std;
int main() {
  double y1, y2, yw, x, y, r;
  while (~scanf("%lf%lf%lf%lf%lf%lf", &y1, &y2, &yw, &x, &y, &r)) {
    double xw = x * (yw - r - r - y1) / (yw + yw - r - r - r - y1 - y);
    if (xw <= 0 || xw >= x) {
      printf("-1\n");
      continue;
    }
    double k = (yw - y1 - r - r) / xw;
    double b = y1 + r;
    double d = fabs(b - y2) / sqrt(k * k + 1);
    if (d >= r)
      printf("%.10lf\n", xw);
    else
      printf("-1\n");
  }
  return 0;
}
