rt

#include<bits/stdc++.h>
using namespace std;
#define int long long
int n,a[100005],l,luchen[100005];
signed main(){
	cin>>n>>l;
	for(int i=1; i<=n; i++)
	    cin>>a[i];
	sort(a+1,a+n+1);
    for(int i=2; i<=n; i++)
        luchen[i]=(a[i]-a[i-1])*1.0;
    luchen[1]=a[1]*2;
    luchen[n+1]=(l-a[n])*2;
    sort(luchen+1,luchen+n+2);
    float ans=luchen[n+1]*1.0/2;
    printf("%0.10f",ans);
	return 0;
}