#include <bits/stdc++.h>
using namespace std;
#pragma comment(linker, "/STACK:64000000")
int n, m, i, j, k, u, v, w;
const int maxn = 100100;
const int maxm = 110;
const int maxmask = 1 << (maxn - 2);
const int infi = 1e9 + 7;
const int mod = 1e9 + 7;
const long long infl = 1e18 + 7;
const double eps = 1e-9;
double y11, y2, x, y, y3, x3, r, res;
void init() { cin >> y11 >> y2 >> y3 >> x >> y >> r; }
void solve() {
  double k = ((y3 - r) - y) / ((y3 - r) - (y11 + r));
  x3 = x / (1.0 + k);
  double s = (y2 - y11 - r) * x3 / 2;
  double h = 2 * s / sqrt(x3 * x3 + (y3 - r - y11 - r) * (y3 - r - y11 - r));
  if ((h - r) <= eps) {
    cout << -1;
  } else {
    printf("%.9f", x3);
  }
}
void out() {}
int main() {
  init();
  solve();
  out();
  return 0;
}
