#include <bits/stdc++.h>
#include <experimental/random>
#include <random>
//#include <ext/pb_ds/assoc_container.hpp>
//using namespace __gnu_pbds;
using namespace std;
using ld = long double;
using ll = long long;
const ll INF = 1e18, MOD = 1e9 + 7;
void solve();
signed main() {
#ifdef LOCAL
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
#endif
ios::sync_with_stdio(false);
cin.tie(0);
int q = 1;
//cin >> q;
while (q--) {
solve();
}
}
void solve() {
ll n, t; cin >> n >> t;
vector<ll> a(n);
for (int i = 0; i < n; i++) {
cin >> a[i];
a[i] %= t;
}
sort(a.begin(), a.end());
for (int i = 0; i < n; i++) {
a.push_back(a[i] + t);
}
ll mx = 0;
for (int i = 1; i < 2 * n; i++) {
mx = max(mx, a[i] - a[i - 1]);
}
cout << mx / 2;
}
