#include <bits/stdc++.h>
using namespace std;
#define endl "\n"
#define int long long
#define pii pair<int, int>
#define ff first
#define ss second
#define entire(x) (x).begin(), (x).end()
const int inf = 1e16;
int32_t main(){
ios::sync_with_stdio(false); cin.tie(nullptr);
int n, k; cin >> n >> k;
vector<int> a(n);
for (int i = 0; i < n; i++) cin >> a[i], a[i] %= k;
// int ans = inf;
// for (int cur = 0; cur < k; cur++){
// int cmax = 0;
// for (auto t : a){
// cmax = max(cmax, min((k - t + cur) % k, k - ((k - t + cur) % k)));
// } ans = min(ans, cmax);
// }
// cout << ans << endl;
int diff = max(a[0], a[1]) - min(a[0], a[1]), ans = (min(diff, k - diff) + 1) / 2;
cout << ans << endl;
return 0;
}
