#include <bits/stdc++.h>
#define int long long
using namespace std;
signed main() {
ios::sync_with_stdio(false);
cin.tie(0);
int tt = 1;
//cin >> tt;
while (tt--) {
int n, t;
cin >> n >> t;
vector<int> a(n);
for (int i = 0;i < n;i++)
cin >> a[i];
sort(a.begin(), a.end());
auto Try = [&](int x) {
int res = 0;
for (int i = 0;i < n;i++) {
if (x >= a[i])
res = max(res, x - a[i]);
else {
int k1 = a[i] - ((a[i] - x) / t * t);
int k2 = a[i] - ((a[i] - x + t - 1) / t * t);
res = max(res, min(abs(x - k1), abs(x - k2)));
}
}
return res;
};
int ans = 1e18, l = 0, r = 1e18;
while (l <= r) {
int mid = (l + r) / 2;
if (min(Try(a[0] - mid), Try(a[0] + mid)) <= mid) {
ans = mid;
r = mid - 1;
}
else
l = mid + 1;
}
cout << ans << '\n';
}
return 0;
}
