#include <bits/stdc++.h>
using namespace std;
#pragma comment(linker, "/STACK:200000000")
const double EPS = 1E-10;
const int INF = 1000000000;
const long long INF64 = (long long)1E18;
const double PI = 3.1415926535897932384626433832795;
int main() {
  double y1, y2, yw, xb, yb, r;
  cin >> y1 >> y2 >> yw >> xb >> yb >> r;
  y1 += r;
  yw -= r;
  double pr = (yw - y1) / (yw - yb);
  double x = xb * pr / (1 + pr);
  x -= 1E-6;
  double a = y1 - yw;
  double b = x;
  double c = -a * x - b * yw;
  double t = sqrt(a * a + b * b);
  a /= t;
  b /= t;
  c /= t;
  if (abs(b * y2 + c) <= r + EPS) {
    puts("-1");
    return 0;
  }
  printf("%.20lf\n", x);
  return 0;
}
