#include <bits/stdc++.h>
using namespace std;
double X, K, B, yy1, yy2, yw, xb, yb, r, delta, sina, tana, len;
int main() {
  scanf("%lf %lf %lf %lf %lf %lf", &yy1, &yy2, &yw, &xb, &yb, &r);
  B = yy1 + r;
  K = (double)((2 * (yw - r) - yb) - B) / (xb);
  X = (double)(yw - r - B) / (K);
  delta = yw - r - yy1 - r;
  tana = (double)X / delta;
  tana = (double)1.0 / tana;
  sina = sqrt((double)1.0 / (1 + tana * tana));
  len = r / sina;
  if (len >= yy2 - yy1 - r)
    cout << -1 << endl;
  else
    printf("%.9lf\n", X);
}
