#include <bits/stdc++.h>
using namespace std;
#define bismillah ios_base::sync_with_stdio(false); cin.tie(0); cout.tie(0);
#define ll long long
#define pll pair<ll, ll>
#define fi first
#define se second
#define pb push_back
#define endl '\n'
ll N, T, a;
void solve() {
    cin >> N >> T;
    
    set<ll> sa;
    vector<ll> va;
    for (int i = 0; i < N; i++) {
        cin >> a;
        sa.insert(a%T);
    }
    for (ll ea : sa) {
        va.pb(ea);
    }
    ll si = va.size();
    for (int i = 0; i < si; i++) {
        va.pb(va[i]+T);
    }
    if (si == 1) {
        cout << 0 << endl;
        return;
    }
    ll mi = T;
    for (int i = 0; i < si; i++) {
        mi = min(mi, (va[i+si-1]-va[i]+1)/2);
    }
    cout << mi << endl;
}
int main() {
    bismillah;
    int Tc = 1;
    // cin >> T;
    for (;Tc--;) solve();
}
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