#include <bits/stdc++.h>
#define ll long long
#define ld long double
using namespace std;

int main()
{
    ll n, x;
    ld ans = (double)-1e18;
    cin >> n >> x;
    vector<ll> v(n);
    for (ll i = 0; i < n; ++i)
        cin >> v[i];
    sort(v.begin(), v.end());
    ld d = v[0];
    if (v[n - 1] <= x)
        if (x - v[n - 1] > d)
            d = x - v[n - 1];
    for (ll i = 1; i < n; ++i)
    {
        ld y = abs(v[i] - v[i - 1] + 0.0) / 2;
        ans = max(ans, y);
    }
    ans = max(ans, d);
    cout << fixed << setprecision(10) << ans << endl;
    return 0;
}