#include <bits/stdc++.h>
using namespace std;
#define int long long
#define ll long long
#define rep(i,a,b) for (int i = a; i <= b; i++)
#define per(i,a,b) for (int i = a; i >= b; i--)
#define fi first
#define se second
#define pii pair<int,int>
#define pb push_back
const int MAXN = 5e5+10;
const int INF = 1e18 + 5;
const int MOD = 1e9+7;
int a[MAXN];
void solve() {
int n,t;cin >> n >> t;
rep(i,1,n) {
cin >> a[i];
a[i] %= t;
}
sort(a+1,a+n+1);
deque<int> q;
rep(i,1,n) q.pb(a[i]);
int ans = INF;
rep(i,1,n) {
ans = min(ans, (q[n-1]-q[0]+1)/2);
int tmp = (q.back()-t);
q.pop_back();
q.push_front(tmp);
}
cout << ans << '\n';
}
int32_t main() {
ios_base::sync_with_stdio(0); cin.tie(nullptr);
int tt = 1;
//cin >> tt;
while (tt--) solve();
return 0;
}
