#include "bits/stdc++.h"

using namespace std;

int main()
{
   
    
    long long int n, max = 0, pos = 0, k, i, j;
    cin >> n;
    cin >> k;
    long long int v[n];
    for (i = 0; i < n; i++)
        cin >> v[i];
    sort(v, v + n);
    for (i = 0; i < n - 1; i++) {
        if ((v[i + 1] - v[i]) >= max) {
            max = v[i + 1] - v[i];
            pos = v[i];
        }
        //out<<max<<" "<<pos<<endl;
    }
    if ((v[0] != 0) && (v[0] >= max/2)) {
        max = 0;
        pos = 0;
    }
    if ((k - v[n - 1]) >= max/2) {
        if ((k - v[n - 1]) >= v[0]) {
            max = 0;
            pos = k;
        }
    }
    cout << (max / 2) + pos;
    

    return 0;
}