#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define ff first
#define ss second
#define all(x) (x).begin(), (x).end()
#define pb push_back
#define ertunt return
const int MOD = 998244353;
#pragma GCC target ("avx2")
#pragma GCC optimization ("O3")
#pragma GCC optimization ("unroll-loops")
int main() {
ll n, t;
cin >> n >> t;
vector<ll> a(2 * n+5);
for (ll i = 0; i < n; i++) {
cin >> a[i];
a[i] %= t;
}
sort(a.begin(), a.begin() + n);
ll ans = 1e14;
for (ll i = 0; i < n; i++) {
ans = min((a[i + n - 1] - a[i] + 1)/2, ans);
a[i + n] = a[i] + t;
}
cout << ans;
}
