#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
using namespace std;
bool sortinrev(const pair<long long int, long long int> &a,
               const pair<long long int, long long int> &b) {
  return (a.first > b.first);
}
long long int A[1000000];
long long int B[1000000];
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ;
  double a, b, c;
  long long int n, k, mx = 0;
  cin >> n >> k;
  for (long long int i = 0; i < n; i++) cin >> A[i];
  sort(A, A + n);
  for (long long int i = 0; i < n - 1; i++) mx = max(mx, (A[i + 1] - A[i]));
  b = mx / 2.0;
  a = (double)(A[0] - 0);
  c = (double)(k - A[n - 1]);
  cout << fixed << setprecision(10) << max(a, max(b, c)) << endl;
  return 0;
}
