#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define MOD 998244353
void solve()
{
ll n, t;
cin >> n >> t;
vector<ll> a(n);
for (int i = 0; i < n; i++)
{
cin >> a[i];
a[i] %= t;
}
sort(a.begin(), a.end());
ll mn = (a[n - 1] + a[0] + 1) / 2;
for (int i = 1; i < n; i++)
{
mn = min(mn, (a[i - 1] + t - a[i] + 1) / 2);
}
cout << mn << '\n';
}
int main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int tests = 1;
// cin >> tests;
for (int i = 1; i <= tests; i++)
solve();
}
