#include <bits/stdc++.h>
using namespace std;
int f[101010];
long long s[101010];
long long a[101010];
int main() {
  ios_base::sync_with_stdio(0);
  long long n, l;
  cin >> n >> l;
  for (int i = 1; i <= n; ++i) cin >> a[i];
  sort(a + 1, a + n + 1);
  if (n == 1) {
    cout << fixed << setprecision(10) << (long double)max(a[1], l - a[1]);
    return 0;
  }
  a[0] = 0;
  long long ans = 0;
  a[n + 1] = l;
  for (int i = 1; i <= n + 1; ++i) ans = max(ans, a[i] - a[i - 1]);
  ans = max(ans, max(a[1] * 2, (a[n + 1] - a[n]) * 2));
  cout << fixed << setprecision(10) << (long double)(ans / 2.0);
  return 0;
}
