#include <bits/stdc++.h>
using namespace std;
template <class F, class T>
T convert(F a, int p = -1) {
  stringstream ss;
  if (p >= 0) ss << fixed << setprecision(p);
  ss << a;
  T r;
  ss >> r;
  return r;
}
template <class T>
T gcd(T a, T b) {
  T r;
  while (b != 0) {
    r = a % b;
    a = b;
    b = r;
  }
  return a;
}
template <class T>
T lcm(T a, T b) {
  return a / gcd(a, b) * b;
}
template <class T>
T sqr(T x) {
  return x * x;
}
template <class T>
T cube(T x) {
  return x * x * x;
}
template <class T>
int getbit(T s, int i) {
  return (s >> i) & 1;
}
template <class T>
T onbit(T s, int i) {
  return s | (T(1) << i);
}
template <class T>
T offbit(T s, int i) {
  return s & (~(T(1) << i));
}
template <class T>
int cntbit(T s) {
  return s == 0 ? 0 : cntbit(s >> 1) + (s & 1);
}
const int bfsz = 1 << 16;
char bf[bfsz + 5];
int rsz = 0;
int ptr = 0;
char gc() {
  if (rsz <= 0) {
    ptr = 0;
    rsz = fread(bf, 1, bfsz, stdin);
    if (rsz <= 0) return EOF;
  }
  --rsz;
  return bf[ptr++];
}
void ga(char& c) {
  c = EOF;
  while (!isalpha(c)) c = gc();
}
int gs(char s[]) {
  int l = 0;
  char c = gc();
  while (isspace(c)) c = gc();
  while (c != EOF && !isspace(c)) {
    s[l++] = c;
    c = gc();
  }
  s[l] = '\0';
  return l;
}
template <class T>
bool gi(T& v) {
  v = 0;
  char c = gc();
  while (c != EOF && c != '-' && !isdigit(c)) c = gc();
  if (c == EOF) return false;
  bool neg = c == '-';
  if (neg) c = gc();
  while (isdigit(c)) {
    v = v * 10 + c - '0';
    c = gc();
  }
  if (neg) v = -v;
  return true;
}
const double PI = acos(-1.0);
const double eps = 1e-9;
const int dr[] = {-1, 0, +1, 0};
const int dc[] = {0, +1, 0, -1};
const int inf = (int)1e9 + 5;
const long long linf = (long long)1e16 + 5;
const long long mod = (long long)1e9 + 7;
int cmp(long double a, long double b) {
  if (abs(a - b) < eps) return 0;
  return a > b ? 1 : -1;
}
struct Point {
  long double x, y;
  Point() {}
  Point(long double _x, long double _y) : x(_x), y(_y) {}
};
void getLine(Point p0, Point p1, long double& a, long double& b,
             long double& c) {
  a = p1.y - p0.y;
  b = p0.x - p1.x;
  c = -(a * p0.x + b * p0.y);
}
long double dist(Point A, long double a, long double b, long double c) {
  return abs(a * A.x + b * A.y + c) / sqrt(sqr(a) + sqr(b));
}
long double Y1, Y2, Yw, xb, yb, r;
int main() {
  cin >> Y1 >> Y2 >> Yw >> xb >> yb >> r;
  long double Y0 = Yw - r;
  Point P(xb, Y0 + Y0 - yb);
  Point Q(0, Y1 + r);
  Point A(0, Y2);
  long double a, b, c;
  getLine(P, Q, a, b, c);
  cout << fixed << setprecision(12);
  if (cmp(dist(A, a, b, c), r) < 0) {
    cout << -1 << endl;
  } else {
    long double x = -(b * Y0 + c) / a;
    cout << x << endl;
  }
  return 0;
}
