#include <bits/stdc++.h>
using namespace std;
const int mod = 1e9 + 7;
long long binPow(long long a, long long b) {
  long long x = 1, y = a;
  while (b) {
    if (b & 1) x = (x * y) % mod;
    y = (y * y) % mod;
    b >>= 1;
  }
  return x % mod;
}
long long inverserEuler(int n) { return binPow(n, mod - 2); }
long long C(int k, int n) {
  vector<long long> f(n + 1, 1);
  for (int i = 2; i <= n; i++) f[i] = (f[i - 1] * i) % mod;
  return (f[n] * ((inverserEuler(f[k]) * inverserEuler(f[n - k])) % mod) %
          mod) %
         mod;
}
long long x, y;
void extendEuclid(long long a, long long b) {
  if (b == 0) {
    x = 1;
    y = 0;
    return;
  }
  extendEuclid(b, a % b);
  long long x1 = y, y1 = x - (a / b) * y;
  x = x1;
  y = y1;
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie();
  int n, l;
  cin >> n >> l;
  int a[n + 1], i, j;
  for (i = 0; i < n; ++i) cin >> a[i];
  a[n] = l;
  n++;
  sort(a, a + n);
  double ans = a[0];
  for (i = 1; i <= n - 2; ++i) ans = max(ans, (a[i] - a[i - 1]) / 2.0);
  ans = max(ans, double(a[n - 1] - a[n - 2]));
  cout << setprecision(9) << fixed << ans;
  return 0;
}
