#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, l;
  int i, a[1008];
  double m, t;
  scanf("%d%d", &n, &l);
  for (i = 0; i < n; i++) {
    scanf("%d", &a[i]);
  }
  if (n == 1) {
    m = (double)(a[0] - 0);
    t = (double)(l - a[0]);
    if (t > m) {
      m = t;
    }
    printf("%.10llf\n", m);
  } else {
    sort(a, a + n);
    m = (double)(a[0] - 0);
    for (i = 1; i < n; i++) {
      while (a[i - 1] == a[i]) {
        i++;
      }
      if (i >= n) break;
      t = (double)(a[i] - a[i - 1]) / 2.0;
      if (t > m) {
        m = t;
      }
    }
    t = (double)(l - a[i - 1]);
    if (t > m) {
      m = t;
    }
    printf("%.10llf\n", m);
  }
  return 0;
}
