#include <bits/stdc++.h>
using namespace std;
#pragma comment(linker, "/STACK:255000000")
bool firstout = 1;
template <class T>
T &minn(T &a, T b) {
  if (b < a) a = b;
  return a;
}
template <class T>
T &maxx(T &a, T b) {
  if (a < b) a = b;
  return a;
}
int &madd(int &a, int b) {
  a += b;
  if (a >= 1000000009) a -= 1000000009;
  return a;
}
int &msub(int &a, int b) {
  a -= b;
  if (a < 0) a += 1000000009;
  return a;
}
int &mmult(int &a, int b) { return a = (long long)a * b % 1000000009; }
int mdiv(long long a, long long b, long long m) {
  a = (a % m + m) % m;
  b = (b % m + m) % m;
  if (a % b == 0) return a / b;
  return (a + m * mdiv(-a, m, b)) / b;
}
int n, m, q;
int A[1012];
int main() {
  int i, j, k;
  char c;
  int a, d;
  int y1, y2, yw, xb, yb, r;
  int ts;
  for (ts = 1; scanf("%"
                     "d",
                     &(y1)) > 0;
       ++ts) {
    scanf(
        "%"
        "d",
        &(y2));
    scanf(
        "%"
        "d",
        &(yw));
    scanf(
        "%"
        "d",
        &(xb));
    scanf(
        "%"
        "d",
        &(yb));
    scanf(
        "%"
        "d",
        &(r));
    int a = yw - r - r - y1;
    int b = yw - r - yb;
    double xw = a * 1. / (a + b) * xb;
    double a1 = 0.;
    double a2 = xw;
    double b1 = y1 + r;
    double b2 = yw - r;
    double A = b2 - b1;
    double B = a1 - a2;
    double C = -a1 * b2 + a2 * b1;
    double d = fabs((B * y2 + C) / hypot(A, B));
    if (d < r)
      printf(
          "%"
          "d",
          (-1)),
          printf("\n"), firstout = 1;
    else
      printf(
          "%"
          ".9lf",
          (xw)),
          printf("\n"), firstout = 1;
  }
  return 0;
}
