#include <bits/stdc++.h>
#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
using namespace std;
template <class T>
ostream &operator<<(ostream &os, const vector<T> &v) {
  os << "[";
  for (int i = 0; i < (((int)(v).size())); ++i) {
    if (i) os << ", ";
    os << v[i];
  }
  return os << "]";
}
template <class T, class U>
ostream &operator<<(ostream &os, const pair<T, U> &p) {
  return os << "(" << p.first << " " << p.second << ")";
}
template <class T>
bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T>
bool chmin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return true;
  }
  return false;
}
using ll = long long;
using ull = unsigned long long;
using ld = long double;
using P = pair<int, int>;
using vi = vector<int>;
using vll = vector<ll>;
using vvi = vector<vi>;
using vvll = vector<vll>;
const ll MOD = 1e9 + 7;
const int INF = INT_MAX / 2;
const ll LINF = LLONG_MAX / 2;
const ld eps = 1e-9;
int gem[30001], sur[30001];
map<int, int> dp[30001];
int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(10);
  int n, d;
  cin >> n >> d;
  for (int i = 0; i < (30001); ++i) gem[i] = 0;
  for (int i = 0; i < (n); ++i) {
    int p;
    cin >> p;
    gem[p]++;
  }
  sur[30000] = gem[30000];
  for (int i = 29999; i >= 0; --i) {
    sur[i] = sur[i + 1] + gem[i];
  }
  if (d == 1) {
    cout << sur[0] << endl;
    return 0;
  }
  dp[d][d] = gem[d];
  int ans = 0;
  for (int i = d; i <= 30000; ++i) {
    vector<bool> noneed(30001);
    vector<int> v(30001);
    for (auto &e : dp[i]) {
      auto [l, val] = e;
      if (noneed[l] && val <= v[l]) continue;
      if (l > 3) {
        for (int j = max(0, 2 * l - 3); j <= min(30000, 2 * l + 3); ++j) {
          noneed[j] = true;
          chmax(v[j], val);
        }
      }
      if (l - 1 > 0 && i + l - 1 <= 30000) {
        if (l - 1 == 1) {
          chmax(ans, val + sur[i + 1]);
        } else {
          chmax(dp[i + l - 1][l - 1], val + gem[i + l - 1]);
        }
      }
      if (i + l <= 30000) {
        chmax(dp[i + l][l], val + gem[i + l]);
      }
      if (i + l + 1 <= 30000) {
        chmax(dp[i + l + 1][l + 1], val + gem[i + l + 1]);
      }
    }
  }
  for (int i = (d); i < (30001); ++i) {
    for (auto &e : dp[i]) {
      chmax(ans, e.second);
    }
  }
  cout << ans << endl;
  return 0;
}
