#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, l, buf[1001];
  double max;
  while (cin >> n && cin >> l) {
    for (int i = 0; i < n; i++) cin >> buf[i];
    sort(buf, buf + n);
    max = (buf[0] == 0) ? 0 : buf[0];
    for (int i = 1; i < n; i++)
      if ((buf[i] - buf[i - 1]) / 2.0 > max) max = (buf[i] - buf[i - 1]) / 2.0;
    if (buf[n - 1] != l && l - buf[n - 1] > max) max = l - buf[n - 1];
    printf("%f\n", max);
  }
  return 0;
}
