#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef vector<vi> vii;
typedef pair<int,int> pi;
typedef vector<pi> pii;
typedef tuple<int,int,int> tii;
#define REP(i,a,b) for(int i=a;i<b;i++)
#define F first
#define S second
#define PB push_back
#define MP make_pair
#define LSOne(s) ((s)&(-s))
ll INF=1e18+10;
int inf=1e9+10;
ll M=1e9+7;
int main() {
//ios::sync_with_stdio(0);
//cin.tie(0);
//freopen("test_input.txt", "r", stdin);
//freopen("test_output.txt", "w", stdout);
int n,m;cin>>n>>m;
vi a(n);
REP(i,0,n)cin>>a[i];
REP(i,0,n)a[i]%=m;
sort(a.begin(),a.end());
//cout<<a[1]<<" ";
int ans=(a[n-1]-a[0]+1)/2;
REP(i,0,n-1)ans=min(ans,(m+a[i]-a[i+1]+1)/2);
cout<<ans;
}
