#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  long long int n, l;
  cin >> n >> l;
  long long int i, a[n], mx;
  if (n == 1) {
    cin >> a[0];
    if (l - a[0] > a[0] - 0)
      cout << l - a[0] << endl;
    else
      cout << a[0] - 0 << endl;
  } else {
    for (i = 0; i < n; i++) cin >> a[i];
    sort(a, a + n);
    mx = a[1] - a[0];
    for (i = 2; i < n; i++) {
      if (a[i] - a[i - 1] >= mx) {
        mx = a[i] - a[i - 1];
      }
    }
    double d = mx / 2.0;
    if (a[0] - 0 > d) d = a[0] - 0;
    if (l - a[n - 1] > d) d = l - a[n - 1];
    cout << setprecision(10) << fixed;
    cout << d << endl;
  }
}
