#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define ordered_set tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update>
using namespace __gnu_pbds;
using namespace std;
#define pb push_back
#define st first
#define nd second
typedef long long ll;
typedef long double ld;
const ll I = 1000LL * 1000LL * 1000LL * 1000LL * 1000LL * 1000LL;
const ll M = 1000LL * 1000LL * 1000LL + 7LL;
const int N = 1000 * 1000 + 7;
int tab[N];
void Solve()
{
int n, t, ans;
cin >> n >> t;
for(int i = 1; i <= n; ++i)
{cin >> tab[i]; tab[i] %= t;}
sort(tab + 1, tab + 1 + n);
ans = (tab[n] - tab[1] + 1) / 2;
for(int i = 1; i < n; ++i)
ans = min(ans, (tab[i] - (tab[i + 1] - t) + 1) / 2);
cout << ans << "\n";
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
//int t; cin >> t;
//while(t--)
Solve();
return 0;
}
