#include "bits/stdc++.h"
using namespace std;
using ll = long long;
#ifdef LOCAL
#include "debug.h"
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
#else
#define debug(...) 42
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
#endif
ll n, T;
ll get(ll t, const vector<ll>& a) {
ll ans = 0;
for(ll x : a) {
ans = max(ans, min((x - t + T) % T, (t - x + T) % T));
}
return ans;
}
void solve() {
cin >> n >> T;
vector<ll> a(n);
for(ll& x : a) {
cin >> x;
x %= T;
}
debug(a);
ll ans = T*n + 37;
for(ll i = 0; i < T; ++i) {
ans = min(ans, get(i, a));
debug(i, get(i,a));
}
cout << ans << "\n";
}
signed main(){
#ifdef LOCAL
freopen("test.in", "r", stdin);
freopen("test.err", "w", stderr);
#endif
ios_base::sync_with_stdio(false);
cin.tie(NULL);
signed T = 1;
// cin >> T;
for(signed test = 1; test <= T; ++test){
solve();
}
}
