#include<bits/stdc++.h>
using namespace std;

#define ll          long long
#define ul          unsigned long long
#define pb          push_back
#define ss          second
#define ff          first
#define fr(m)       for(int i=0; i<m; ++i)
#define fro(m)      for(int i=1; i<m; ++i)
#define frj(m)      for(int j=0; j<m; ++j)
#define frr(n)      for(int i=n; i>=0; --i)
#define nl          '\n'
#define yes         cout<<"YES"<<nl
#define no          cout<<"NO"<<nl
#define all(x)      x.begin(), x.end()
#define dbg(x)    cerr << #x <<" "<< x << endl;
#define fast_io  (ios_base:: sync_with_stdio(false),cin.tie(NULL));

ll fact(ll n){ if(n==0) return 1; ll res = 1; for (ll i = 2; i <= n; i++) res = res * i; return res;}
ll nPr(ll n, ll r) { return fact(n) / fact(n - r); }
ll nCr(ll n, ll r) { return fact(n) / (fact(r) * fact(n - r)); }
ll gcd(ll a, ll b) { if (b == 0) return a; return gcd(b, a % b); }
ll lcm(ll a, ll b) { return (a * b) / gcd(a, b);}
ll mypow(ll a, ll b){ ll ans = 1; while(b){ if (b&1) ans = (ans*a) ; b /= 2; a = (a*a); } return ans; }
bool isPrime(ll n) { if(n <= 1) return false; for(ll i = 2; i <= sqrt(n); i++) if(n % i == 0) return false; return true;}

#define PI          3.141592653589793238;
#define INF         LONG_LONG_MAX;
#define MOD         1e9+7;

//////////////////////////////////Code Start/////////////////////////////////////

void solve()
{
    int n,l;
    cin>>n>>l;
    vector<int>lamps(n);
    fr(n)
        cin>>lamps[i];
    int mx=0;
    sort(all(lamps));
    fro(n)
    {
        int x=lamps[i]-lamps[i-1];
        mx=max(x,mx);
    }
    cout<<showpoint<<fixed<<setprecision(10);
    double dis=max(lamps[0]-0, l - lamps[n - 1]);
    cout<<max(dis,(double)mx/2)<<nl;
}
 
int main()
{
    fast_io;
    int TC = 1;
    //cin >> TC;
    while (TC--) solve();
}