#include <bits/stdc++.h>
using namespace std;
// #define int long long
#define ll long long
#define ff first
#define ss second
#define pint pair < int , int >
#define fast ios_base::sync_with_stdio(NULL); cin.tie(NULL)
typedef vector < int > vint;
const int inf = 1e9 + 9;
const int mxn = 5e5 + 2;
const int mod = 1e9 + 7;
int a[mxn];
int main() {
int n , t;
cin >> n >> t;
for (int i = 0; i < n; i++) {
cin >> a[i];
a[i] %= t;
}
sort(a , a + n);
int ans = a[n-1] - a[0];
for (int i = n-1; i >= 1; i--) {
ans = min(ans , a[i-1] - (a[i] - t));
}
cout << (ans + 1) / 2 << '\n';
return 0;
}
