// #include <bits/stdc++.h>
#include <iostream>
#include <cmath>
#include <algorithm>
#include <map>
#include <unordered_map>
#include <vector>
#include <iomanip>
#include <string>
#include <queue>
#include <set>
#include <deque>
using namespace std;
#define int long long
#define endl "\n"
#define fi first
#define se second
const int M=998244353;
const int inf = 1e16;
const int LOG=20;
const int N=2e5+5;
int n , m , c , w , k , t=1 , q=1 , x , y , z , l , r;
void solve()
{
cin >> n >> k;
vector<int>a(n);
for (int i=0;i<n;i++){
cin >> a[i];
a[i]%=k;
}
sort(a.begin(),a.end());
int mn=a[0];
int mx=a[n-1];
c=(mx-mn+1)/2;
for (int i=1;i<n;i++){
mn=a[i];
mx=a[i-1]+k;
c=min(c,(mx-mn+1)/2);
}
cout << c << endl;
}
signed main()
{
ios::sync_with_stdio(0);//DO NOT USE IN INTERACTIVE
cin.tie(0), cout.tie(0);//DO NOT USE IN INTERACTIVE
cout << fixed << setprecision(9);
srand(time(0));
// int t=1;
// cin >> t;
for (int _=1;_<=t;_++){
solve();
q++;
}
}
