#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#define fi first
#define sc second
#define pb push_back
#define int long long
using namespace std;
using namespace __gnu_pbds;
typedef long long ll;
typedef double db;
typedef pair<int, int> pii;
template<typename type>
using ordered_set = tree<type, null_type, less<type>, rb_tree_tag, tree_order_statistics_node_update>;
const int N = 5e5 + 5, mod = 1e9 + 7, inf = 2e9;
const int dl[] = {-1, 0, 1, 0}, dc[] = {0, 1, 0, -1};
const int ddl[] = {-1, -1, -1, 0, 1, 1, 1, 0}, ddc[] = {-1, 0, 1, 1, 1, 0, -1, -1};
mt19937 gen(chrono::steady_clock::now().time_since_epoch().count());
int rng(int lo = 1, int hi = INT_MAX) {
uniform_int_distribution<int> rnd(lo, hi);
return rnd(gen);
}
struct mint {
int val;
mint(int32_t x = 0) {
val = x % mod;
}
mint(long long x) {
val = x % mod;
}
mint operator+(mint x) {
return val + x.val;
}
mint operator-(mint x) {
return val - x.val + mod;
}
mint operator*(mint x) {
return 1LL * val * x.val;
}
void operator+=(mint x) {
val = (*this + x).val;
}
void operator-=(mint x) {
val = (*this - x).val;
}
void operator*=(mint x) {
val = (*this * x).val;
}
friend auto operator>>(istream& in, mint &x) -> istream& {
in >> x.val;
x.val %= mod;
return in;
}
friend auto operator<<(ostream& out, mint const &x) -> ostream& {
out << x.val;
return out;
}
};
int n, m, a[N];
int32_t main()
{
cin.tie(nullptr)->sync_with_stdio(0);
cin >> n >> m;
for(int i=1; i<=n; i++)
cin >> a[i], a[i] %= m;
sort(a+1, a+n+1);
int med, ans = 0;
for(int bulan=1; bulan<=20; bulan++) {
if(abs(a[1] - a[n]) > abs(a[1] - a[n] + m))
a[n] -= m;
med = (a[1] + a[n]) / 2;
for(int i=1; i<=n; i++)
if(abs(a[i]-med) > abs(a[i]-m-med))
a[i] -= m;
}
for(int i=1; i<=n; i++)
ans = max(ans, abs(a[i]-med));
cout << ans;
return 0;
}
