#include <bits/stdc++.h>
#define ff first
#define ss second
#define MOD 998244353
#define INF 1000000009
#define ld long double
#define pb push_back
#define ll long long
using namespace std;
ll n,a,b,c,d,ans=INF,ak;
deque<pair<ll,ll>>q;
vector<pair<ll,ll>>v;
int main()
{
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
cin>>n>>a;
for(int i=0;i<n;i++){
cin>>b;
v.pb({b%a,b});
}
sort(v.begin(),v.end());
for(int i=0;i<n;i++){
q.pb(v[i]);
}
for(int i=0;i<n+2137;i++){
ans=min(ans,q.back().ff-q.front().ff);
q.pb({q.front().ff+a,q.front().ss});
q.pop_front();
}
cout<<(ans+1)/2;
}
