#include <bits/stdc++.h>
using namespace std;
#define int long long
#define endl '\n'
signed main(){
int n, t; cin >> n >> t;
int a[n + 1];
for (int i = 1; i <= n; i++){
cin >> a[i];
a[i] %= t;
// cout << a[i] << ' ';
}
// int ma = 0, mi = 2 * t;
// cout << endl;
int ans = 0;
for (int i = 1; i <= n; i++){
int dist = 0;
for (int j = 1; j <= n; j++){
int m1 = abs(a[i] - a[j]), m2 = min(abs(a[i] - (a[j] + t)), abs((a[i] + t) - a[j]));
dist = max(dist, min(m1, m2));
// if (i == 1) cout << m1 << ' ' << m2 << endl;
}
ans = max(ans, dist);
}
cout << (ans + 1) / 2 << endl;
return 0;
}
