#include <bits/stdc++.h>
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define int long long
#define yes() cout << "YES\n"
#define no() cout << "NO\n"
using namespace std;
using ll = long long;
using ull = unsigned long long;
using ld = long double;
const int inf = 1e18;
const int mod = 1e9 + 7;
const int maxn = 1e6;
const int mod1 = 998244353;
const int mod2 = 1e18 + 1;
const int mod3 = 1e9 + 9;
const int mod4 = 333333333;
const int mod5 = 200000;
const int mod6 = 10007;
const int k = 3000;
const int w = 1e5;
const ld EPS = 1e-8;
int LOG = 30;
void solve() {
int n, k;
cin >> n >> k;
vector<int> a(n);
for (int& i : a) cin >> i;
// sort(all(a));
int ans = inf;
for (int i = 0; i < k; i++) {
int x = i;
int sum = 0;
for (int& j : a) {
int y = abs(x - j) % k;
sum = max(sum, min(y, k - y));
}
ans = min(ans, sum);
}
cout << ans << "\n";
}
signed main() {
// cout.precision(16);
ios::sync_with_stdio(false);
cin.tie(nullptr);
int t = 1;
// cin >> t;
while (t--) {
solve();
}
}
