// #include <me>
#include <bits/stdc++.h>
using namespace std;
#define endl "\n"
#define pb push_back
#define int long long
const int N = 3e3 + 5, M = 1e9 + 7, LG = 20;
int n , T , x , y , A[N];
void solve(){
cin >> n >> T;
for (int i = 1 ; i <= n ; i++){
cin >> A[i];
}
int ans = 1e18;
for (int i = 0 ; i <= T ; i++){
int mx = -1e18;
for (int j = 1 ; j <= n ; j++){
mx = max(mx , min(abs(i - A[j]%T) , abs(T - (i - A[j]%T))));
}
ans = min(ans , mx);
}
cout << ans << endl;
}
signed main(){
ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
int ts = 1;
// cin >> ts;
while(ts--){
solve();
}
}
