#include <cstdio>
#include <stdio.h>
#include <stdbool.h>
#include <iostream>
#include <map>
#include <vector>
#include <climits>
#include <stack>
#include <string>
#include <queue>
#include <algorithm>
#include <set>
#include <unordered_set>
#include <unordered_map>
#include <cmath>
#include <cctype>
#include <bitset>
#include <iomanip>
#include <cstring>
#include <numeric>
#include <cassert>
#include <random>
#include <chrono>
#include <fstream>
using namespace std;
#define int long long
#define pii pair<int, int>
#define mp make_pair
#define pb push_back
#define fi first
#define se second
int32_t main(){
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
int n, k;
cin>>n>>k;
vector<int> vect(n);
for (int i=0; i<n; ++i)cin>>vect[i], vect[i]%=k;
sort(vect.begin(), vect.end());
int mx=vect[0]-vect.back()+k;
for (int i=1; i<n; ++i)mx=max(mx, vect[i]-vect[i-1]);
cout<<(k-mx+1)/2;
}
