# include <bits/stdc++.h>
# define int long long
# define vi vector<int>
# define pb push_back
# define pii pair<int, int>
# define fi first
# define se second
# define endl '\n'
# define jess ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
using namespace std;
int n, t, a[500005];
void solve () {
cin >> n >> t;
for(int i=1; i<=n; i++) {
cin >> a[i];
a[i]%=t;
}
sort(a+1, a+n+1);
int ans=(a[n]-a[1]+1)/2, mn=a[1];
for(int i=n; i>=2; i--) {
mn=min(mn, a[i]-t);
ans=min(ans, (a[i-1]-mn+1)/2);
}
cout << ans << endl;
}
signed main() {
jess;
solve();
}
