#include <bits/stdc++.h>
using std::printf;
using std::scanf;
using std::sqrt;
int xb, yb, yw, yy1, y2, xrf, r;
double xw;
bool success;
void aim() {
  int yr = yw - r;
  int y1ref = 2 * yr - yy1;
  int y2ref = 2 * yr - y2;
  double yAim = y1ref - r;
  double ydiff = yAim - yb;
  double xbd = xb;
  double c = sqrt(ydiff * ydiff + xbd * xbd) / xbd;
  double projectedR = r * c;
  if (projectedR + r < y1ref - y2ref) {
    xw = xb * (yAim - yr) / (yAim - yb);
    success = true;
  } else
    success = false;
}
void readInput() { scanf("%d %d %d %d %d %d", &yy1, &y2, &yw, &xb, &yb, &r); }
int main() {
  readInput();
  aim();
  if (success) {
    printf("%.15f\n", xw);
  } else
    printf("-1\n");
}
