#include <bits/stdc++.h>
using namespace std;
int main() {
  long long l, j, x, y, lar = 0;
  int n, i;
  cin >> n >> l;
  long long a[n], sm[n + 2];
  long long big = 0;
  for (i = 0; i < n; i++) {
    cin >> a[i];
  }
  sm[n + 1] = 0;
  sm[n] = 0;
  sort(a, a + n);
  if (a[0] != 0) {
    sm[n] = a[0] * 2;
  }
  if (a[n - 1] != l) {
    sm[n + 1] = (l - a[n - 1]) * 2;
  }
  sm[0] = a[1] - a[0];
  sm[n - 1] = a[n - 1] - a[n - 2];
  for (i = 1; i < n - 1; i++) {
    x = a[i] - a[i - 1];
    y = a[i + 1] - a[i];
    sm[i] = (x > y) ? x : y;
  }
  for (i = 0; i < n + 2; i++) {
    big = (big < sm[i]) ? sm[i] : big;
  }
  double bigga = big / 2.0;
  printf("%f\n", bigga);
  return 0;
}
