#include <bits/stdc++.h>
using namespace std;
char buf[1 << 21], *p1 = buf, *p2 = buf;
template <class T>
void read(T &x) {
  x = 0;
  int c = getchar();
  int flag = 0;
  while (c < '0' || c > '9') flag |= (c == '-'), c = getchar();
  while (c >= '0' && c <= '9')
    x = (x << 3) + (x << 1) + (c ^ 48), c = getchar();
  if (flag) x = -x;
}
template <class T>
T _max(T a, T b) {
  return b < a ? a : b;
}
template <class T>
T _min(T a, T b) {
  return a < b ? a : b;
}
template <class T>
bool checkmax(T &a, T b) {
  return a < b ? a = b, 1 : 0;
}
template <class T>
bool checkmin(T &a, T b) {
  return b < a ? a = b, 1 : 0;
}
double sqr(double x) { return x * x; }
double jzyakioi, hcyakioi, yw, xb, yb, r;
void init() {
  scanf("%lf%lf%lf%lf%lf%lf", &jzyakioi, &hcyakioi, &yw, &xb, &yb, &r);
}
void solve() {
  double p = yw - r - yb, q = yw - jzyakioi - r - r;
  double x = xb * q / (p + q);
  double d = (hcyakioi - jzyakioi - r) * x / sqrt(sqr(x) + sqr(q));
  if (r > d)
    printf("-1\n");
  else
    printf("%.14lf\n", x);
}
int main() {
  init();
  solve();
  return 0;
}
