#include <bits/stdc++.h>
using namespace std;
#define forn(i,n) for(int i=0;i<int(n);i++)
#define forsn(i,s,n) for(int i=int(s);i<int(n);i++)
#define dforn(i,n) for(int i=int(n)-1;i>=0;i--)
#define dforsn(i,s,n) for(int i=int(n)-1;i>=int(s);i--)
#define fst first
#define snd second
#define pb push_back
#define eb emplace_back
#define sz(x) (int)x.size()
#define all(x) x.begin(), x.end()
typedef long long ll;
typedef vector<ll> vll;
typedef vector<int> vi;
typedef pair<int,int> ii;
int main(){
ios::sync_with_stdio(0);
cin.tie(0);
int n,t;
cin>>n>>t;
vi a(n);
forn(i,n) cin>>a[i];
forn(i,n) a[i]%=t;
sort(all(a));
if(a.front()==a.back()){
cout<<"0\n";
return 0;
}
int ans=t;
forn(i,n){
int mini=a[i];
int maxi=a[(i+n-1)%n];
if(maxi<=mini) maxi+=t;
int mid=(mini+maxi)/2;
ans=min(ans,max(maxi-mid,mid-mini));
}
cout<<ans<<'\n';
return 0;
}
