#include <bits/stdc++.h>
#define int long long int
#define F first
#define S second
#define pb push_back
#define mp make_pair
#define pi pair<int, int>
#define INF 1e18
using namespace std;
int N, T, A[500010], mn = INF, hi = INF, mxd = -INF, mnd = INF;
// multiset<int> ms;
// once someone reaches half of T, flip them
// use a multiset???
int32_t main() {
ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
cin >> N >> T;
for (int i = 0; i < N; i++) {
cin >> A[i];
mn = min(mn, A[i]);
}
for (int i = 0; i < N; i++) {
int m = (A[i] - mn) % T;
int d = min(m, T - m);
}
for (int j = 0; j < N; j++) {
int m = (A[j] - mn) % T;
int d = m;
if (abs(m) <= abs(T - m)) d = m;
else d = T - m;
mxd = max(mxd, d);
mnd = min(mnd, d);
// cout << d << " ";
}
cout << (mxd - mnd) / 2 + ((mxd - mnd) % 2 != 0) << "\n";
// for (int j = 0; j < N; j++) {
// int m = (A[j] - i) % T;
// int d = min(abs(m), abs(T - m));
// mxd = max(mxd, d);
// ms.insert(d);
// }
// incr by 1 each time
// until > half then flip
// for (int i = mn - T / 2; i <= mn + T / 2; i++) {
// int mxd = -INF;
// for (int j = 0; j < N; j++) {
// int m = (A[j] - i) % T;
// int d = min(abs(m), abs(T - m));
// mxd = max(mxd, d);
// cout << d << " ";
// }
// cout << endl;
// hi = min(hi, mxd);
// }
// cout << hi << "\n";
return 0;
}
