#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;
    }
    sort(begin(a),end(a));
    a.resize(unique(begin(a), end(a)) - begin(a));
    n = size(a);
    // if(a[0] == a[n-1] or T == 1) {
    //     cout << 0 << "\n";
    //     return;
    // }
    debug(a);
    ll ans = T*n + 37;
    for(ll i = 0; i < n; ++i) {
        ll l = a[i], r = a[(i+1) % n];
        ll cur = (l - r + T) % T;
        debug(l,r,cur);
        ans =  min(ans, cur/2 + cur%2);
    }
    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();
    }
}
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