#include <bits/stdc++.h>   using namespace std;   const int N = 3e4, INF = int(1e9) + 1, mod = 1e9 + 7;   const long long BIG = 1e16;   int n, d, a[N + 5], dp[N + 5][250 * 2 + 5];   bool w[N + 5][250 * 2 + 5];   int rec(int v, int l) {     if (v > N) {       return 0;     }     int l1 = l - (d - 250);     if (w[v][l1]) return dp[v][l1];     int ans = 0;     for (int i = -1; i <= 1; i++) {       if (l + i) ans = max(ans, rec(v + l + i, l + i));     }     w[v][l1] = 1;     ans += a[v];     return dp[v][l1] = ans;   }   int main() {     ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);     cin >> n >> d;     for (int i = 1; i <= n; i++) {       int x;       cin >> x;       a[x]++;     }     cout << rec(d, d);   }   