#include <bits/stdc++.h>
using namespace std;
double max(double a, double b, double c) {
  if (a >= b) {
    if (a >= c) {
      return a;
    } else {
      return c;
    }
  } else {
    if (b >= c) {
      return b;
    } else {
      return c;
    }
  }
}
int main() {
  long long n, l;
  cin >> n >> l;
  double a[n], b[n];
  for (int i = 0; i < n; i++) {
    cin >> a[i];
  }
  sort(a, a + n);
  for (int i = 1; i < n; i++) {
    b[i - 1] = a[i] - a[i - 1];
  }
  double tmp = *max_element(b, b + n - 1) / 2;
  double ans1, ans2, ans3;
  ans1 = ans2 = ans3 = 0;
  double temp = (l - a[n - 1]);
  ans1 = a[0];
  ans2 = temp;
  ans3 = *max_element(b, b + n - 1) / 2;
  cout << fixed << setprecision(10) << max(ans1, ans2, ans3);
}
