#include <bits/stdc++.h>
using namespace std;
int main() {
  vector<int> v;
  int n, l;
  cin >> n >> l;
  int a[n];
  for (int i = 0; i < n; i++) cin >> a[i];
  sort(a, a + n);
  int c1 = count(a, a + n, 0);
  int c2 = count(a, a + n, l);
  if (n == 1) {
    if (a[0] == l || a[0] == 0)
      cout << l;
    else {
      if (a[0] >= (l - a[0]))
        cout << a[0];
      else
        cout << l - a[0];
    }
  } else {
    if (c1 != 0 && c2 != 0) {
      for (int i = 0; i < n - 1; i++) v.push_back(a[i + 1] - a[i]);
      int max1 = *max_element(v.begin(), v.end());
      double ans = (double)max1 / 2;
      cout << fixed;
      cout << setprecision(9);
      cout << ans;
    } else if (c1 == 0 && c2 != 0) {
      for (int i = 0; i < n - 1; i++) v.push_back(a[i + 1] - a[i]);
      int max1 = *max_element(v.begin(), v.end());
      double ans = (double)max1 / 2;
      if (ans >= a[0]) {
        cout << fixed;
        cout << setprecision(9);
        cout << ans;
      } else
        cout << a[0];
    } else if (c1 != 0 && c2 == 0) {
      for (int i = 0; i < n - 1; i++) v.push_back(a[i + 1] - a[i]);
      int max1 = *max_element(v.begin(), v.end());
      double ans = (double)max1 / 2;
      if (ans >= (l - a[n - 1])) {
        cout << fixed;
        cout << setprecision(9);
        cout << ans;
      } else
        cout << (l - a[n - 1]);
    } else {
      v.push_back(a[0]);
      for (int i = 0; i < n - 1; i++) v.push_back(a[i + 1] - a[i]);
      int max1 = *max_element(v.begin(), v.end());
      double ans = (double)max1 / 2;
      if (a[0] >= (l - a[n - 1])) {
        if (ans >= a[0]) {
          cout << fixed;
          cout << setprecision(9);
          cout << ans;
        } else
          cout << a[0];
      } else {
        if (ans >= (l - a[n - 1])) {
          cout << fixed;
          cout << setprecision(9);
          cout << ans;
        } else
          cout << (l - a[n - 1]);
      }
    }
  }
}
