#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/detail/standard_policies.hpp>
#define ll long long
#define ld long double
#define endl "\n"
#define yeap cout<<"YES"<<endl
#define nope cout<<"NO"<<endl
#define all(v) v.begin(), v.end()
using namespace std;
using namespace __gnu_pbds;
template<class T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
template<class T> using ordered_multiset = tree<T, null_type, less_equal<T>, rb_tree_tag, tree_order_statistics_node_update>;
const ll infp = 1e18;
const ll infn = 1e18 * (-1);
const ll N = 2e5 + 10;
const ll M = 5e3 + 10;
const ll MOD = 998244353;
ll hceil(ll a, ll b){
return (a+b-1)/b;
}
void solve(ll testcase){
ll n, t;
cin>>n>>t;
ll arr[n];
set<ll> st;
for(int i=0; i<n; i++){
cin>>arr[i];
ll temp = arr[i] % t;
st.insert(temp);
}
vector<ll> v;
for(auto u : st){
// cout << u << " ";
v.push_back(u);
}
// cout << endl;
ll a = v[0];
ll mx_dist = infn;
vector<ll> idxs;
for(int i=0; i<v.size(); i++){
ll p1 = ((v[i] - a) % t + t) % t;
ll p2 = ((a - v[i]) % t + t) % t;
// cout << a << " " << p1 << " " << p2 << endl;
ll temp = min(p1, p2);
if(temp < mx_dist){
continue;
} else if(temp > mx_dist){
mx_dist = temp;
idxs.clear();
idxs.push_back(i);
} else if(temp == mx_dist){
idxs.push_back(i);
}
}
ll ans = infn;
for(int i=0; i<idxs.size(); i++){
a = v[idxs[i]];
for(int j=0; j < v.size(); j++){
ll p1 = ((v[j] - a) % t + t) % t;
ll p2 = ((a - v[j]) % t + t) % t;
ans = max(ans, min(p1, p2));
}
}
cout << hceil(ans, 2LL) << endl;
}
int main(){
#if __has_include("LOCAL.hh")
#include "LOCAL.hh"
#endif
#ifdef LOCAL
freopen("input.txt", "r", stdin);
freopen("output3.txt", "w", stdout);
using namespace std::chrono;
cout << fixed << setprecision(9);
auto begin = steady_clock::now();
#else
std::ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
#endif
int T = 1;
//cin>>T;
for(int i=1; i<=T; i++){
solve(i);
}
#ifdef LOCAL
auto end = steady_clock::now();
cout << "\nTime : "
<< (ld)duration_cast<nanoseconds>
(end - begin).count()/1000000000
<< "s" << endl;
#endif
return 0;
}
