//#pragma optimize("Ofast")
//#pragma optimize("unroll-loops")
//#pragma traget("avx,avx2")
#include <iostream>
#include <cmath>
#include <algorithm>
#include <stdio.h>
#include <cstdint>
#include <cstring>
#include <string>
#include <cstdlib>
#include <vector>
#include <bitset>
#include <map>
#include <queue>
#include <ctime>
#include <stack>
#include <set>
#include <list>
#include <random>
#include <deque>
#include <functional>
#include <iomanip>
#include <sstream>
#include <fstream>
#include <complex>
#include <numeric>
#include <cassert>
#include <array>
#include <tuple>
#include <unordered_map>
#include <unordered_set>
#include <thread>
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
#define el '\n'
#define ff first
#define ss second
#define pb push_back
#define pf push_front
#define popb pop_back
#define popf pop_front
#define point pair <ll, ll>
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
using namespace std;
#include <random>
mt19937 rnd(time(0));
const ll INF = 2e18 + 10;
const ll inf = 1e9 + 10;
const ll N = 3e5 + 10;
const ll mod = 1e9 + 7;
const ll LOG = 20;
void solve() {
ll n, t;
cin >> n >> t;
vector <ll> a(n);
for (ll i = 0; i < n; i++)
cin >> a[i];
sort(all(a));
ll ans = 0;
for (ll i = 1; i < n; i++)
ans = max(ans, min((a[i] - a[0]) % t, t - (a[i] - a[0]) % t));
cout << (ans + 1) / 2 << el;
return;
}
signed main() {
ios_base::sync_with_stdio(0);
cin.tie(0); cout.tie(0);
//freopen("deleg.in", "r", stdin);
//freopen("deleg.out", "w", stdout);
int tests = 1;
//cin >> tests;
while (tests--)
solve();
return 0;
}
/*
*/
