#include <bits/stdc++.h>
#pragma comment(linker, "/STACK:16777216")
using namespace std;
int n, l, a[200100];
int main() {
  ios::sync_with_stdio(0);
  while (cin >> n >> l) {
    for (int i = 0; i < n; ++i) cin >> a[i];
    sort(a, a + n);
    int res = max(a[0] * 2, (l - a[n - 1]) * 2);
    for (int i = 1; i < n; ++i) res = max(res, a[i] - a[i - 1]);
    cout << res / 2;
    if (res % 2)
      puts(".50000000");
    else
      puts(".0000000");
  }
  return 0;
}
