///HELLO THERE~!
///CREATED BY MD SADMAN MEHEDI SIVAN(IUT CSE-SWE^19)

#include <bits/stdc++.h>

#define fastio ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define read freopen("blue.txt","r",stdin);
#define write freopen("red.txt","w",stdout);
#define pie 2*acos(0.0);

typedef long long ll;

using namespace std;

int main()
{
    fastio;

    int n,l;
    cin>>n>>l;

    int sivan[n+1];
    for(int i=0; i<n; i++)
        cin>>sivan[i];

    float f=0;
    float r;

    sort(sivan,sivan+n);

    float a=(float)sivan[0]-0;
    float b=l-(float)sivan[n-1];
    float bakon=max(a,b);

    for(int i=0; i<n-1; i++)
    {
        r=(float)sivan[i+1]-sivan[i];
        if(r>=f)
            f=r;

    }

    float q=(f/2.0);


    if(bakon>q)
        cout<<fixed<<setprecision(10)<<bakon;
    else
        cout<<fixed<<setprecision(10)<<q;


    return 0;

}