text: #include <bits/stdc++.h>
  using namespace std;
  
  const int MAXN = 1010;
  
  int main(){
  	ios_base::sync_with_stdio(0);
  	int n, i, l, A[MAXN], d = -123;
  	cin >> n >> l;
  	for(i = 0; i < n; i++){
  		cin >> A[i];
  	}
  	sort(A, A+n);
  	for(i = 1; i < n; i++){
  		d = max(d, A[i] - A[i-1]);
  	}
  	printf("%.10lf\n", max((double)(d/2.0), max((double)A[0], (double)(l-A[n-1]))));
  }
  