#include <bits/stdc++.h>
using namespace std;
int main() {
  long long n, t;
  cin >> n >> t;
  long long arr[n];
  for (int i = 0; i < n; i++) {
    cin >> arr[i];
  }
  sort(arr, arr + n);
  float mxdif = INT_MIN;
  for (int i = 1; i < n; i++) {
    if (arr[i] - arr[i - 1] > mxdif) {
      mxdif = arr[i] - arr[i - 1];
    }
  }
  double z = (mxdif + 0.000) / 2;
  double maxcnr = max(arr[0] - 0, t - arr[n - 1]);
  printf("%.9lf", max(z, maxcnr));
  return 0;
}
