#include <bits/stdc++.h>
#pragma comment(linker, "/STACK:100000000,100000000")
using namespace std;
const long long inf = 1e18 + 7;
const long long mod = 1e9 + 7;
const double eps = 1e-10;
const double PI = 2 * acos(0.0);
const double E = 2.71828;
long double r, yw;
inline void ans(long double x0, long double y0, long double x1, long double y1,
                long double y) {
  long double a = y0 - y1;
  long double b = x1 - x0;
  long double c = x0 * y1 - x1 * y0;
  long double dist = b * y + c;
  if (dist < 0) dist = -dist;
  if (dist / sqrt((a * a + b * b)) > r) {
    cout << setprecision(10) << fixed << (-b * yw - c) / a - eps << endl;
  } else
    cout << -1 << endl;
}
int main(void) {
  long double y1, y2, xb, yb;
  cin >> y1 >> y2 >> yw >> xb >> yb >> r;
  yw -= r;
  yb = 2 * yw - yb;
  ans(xb, yb, 0, y1 + r, y2);
  return 0;
}
