#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, l;
  cin >> n >> l;
  int a[n];
  for (int i = 0; i < n; i++) {
    cin >> a[i];
  }
  sort(a, a + n);
  double maximum = INT_MIN;
  int position = a[0];
  for (int i = 1; i < n; i++) {
    if (maximum < a[i] - position) {
      maximum = a[i] - position;
    }
    position = a[i];
  }
  double start = a[0], end = l - a[n - 1];
  if (start >= maximum / 2 && start >= end) {
    printf("%0.10f", start);
  } else if (end >= start && end >= maximum / 2) {
    printf("%0.10f", end);
  } else {
    printf("%0.10f", maximum / 2);
  }
}
