#include<bits/stdc++.h>
#include <ext/pb_ds/tree_policy.hpp>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/rope>
using namespace std;
using namespace __gnu_pbds;
using namespace __gnu_cxx;

#define mod 1000000007
 /*
    /\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/ *** Debugging Start *** \/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/
*/
void __print(int x) {cerr << x;}
void __print(long x) {cerr << x;}
void __print(long long x) {cerr << x;}
void __print(unsigned x) {cerr << x;}
void __print(unsigned long x) {cerr << x;}
void __print(unsigned long long x) {cerr << x;}
void __print(float x) {cerr << x;}
void __print(double x) {cerr << x;}
void __print(long double x) {cerr << x;}
void __print(char x) {cerr << '\'' << x << '\'';}
void __print(const char *x) {cerr << '\"' << x << '\"';}
void __print(const string &x) {cerr << '\"' << x << '\"';}
void __print(bool x) {cerr << (x ? "true" : "false");}
template<typename T, typename V>
void __print(const pair<T, V> &x) {cerr << '{'; __print(x.first); cerr << ','; __print(x.second); cerr << '}';}
template<typename T>
void __print(const T &x) {int f = 0; cerr << '{'; for (auto &i: x) cerr << (f++ ? "," : ""), __print(i); cerr << "}";}
void _print() {cerr << "]\n";}
template <typename T, typename... V>
void _print(T t, V... v) {__print(t); if (sizeof...(v)) cerr << ", "; _print(v...);}
#ifndef ONLINE_JUDGE
#define debug(x...) cerr << "[" << #x << "] = ["; _print(x)
#else
#define debug(x...)
#endif
/*
    /\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/ *** Debugging Ends *** \/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/
*/
using namespace __gnu_pbds;
template <typename T>
using ordered_set = tree<T, null_type, less_equal<T>, rb_tree_tag, tree_order_statistics_node_update>;

/// Some frequent usable functions
#define int                        long long
void add(int &a,int b){a+=b;if(a>mod)a-=mod;}
void sub(int &a,int b){a-=b;if(a<0)a+=mod;}
void mul(int &a, int b) {a=1ll * a * b % mod;}
template<typename T> T pow(T a,T b, long long m){T ans=1; while(b>0){ if(b%2==1) ans=(ans*a)%m; b/=2; a=(a*a)%m; } return ans%m; }
int powmod(int a,int b)
{int res = 1;while(b){if(b&1){res = (res * a)%mod;}b= b/2;a = (a*a)%mod;}return res;}
int _ceil(int, int);
int _floor(int a, int b) { return b < 0 ? _floor(-a, -b) : a < 0 ? -_ceil(-a, b) : a / b; }
int _ceil(int a, int b) { return b < 0 ? _ceil(-a, -b) : a < 0 ? -_floor(-a, b) : (a + b - 1) / b; }

// int gcd(int a, int b, int &x, int &y) {if (a == 0) {x = 0; y = 1;return b;
//     }int x1, y1;int d = gcd(b%a, a, x1, y1); x = y1 - (b / a) * x1;y = x1;return d;}
// int find(int v){return v==parent[v]?v:parent[v] = find(parent[v]);}
// void merge(int i,int j)
//     {i = find(i);j = find(j);if(i == j)return;parent[parent[i]] = parent[j];cmp--;}

/*
    /\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/ *** Directions in grids *** \/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/
*/
// int dy[4] = {0,0,1,-1}, dx[4] = {1,-1,0,0}; // 4 Direction
// int dx[] = {1,-1,0,0,1,1,-1,-1} , dy[] = {0,0,1,-1,1,-1,1,-1};  // 8 Direction
// int dx[] = {1,-1,1,-1,2,2,-2,-2} , dy[] = {2,2,-2,-2,1,-1,1,-1};  // Knight moves
// int dx[] = {2,-2,1,1,-1,-1} , dy[] = {0,0,1,-1,1,-1};  // Hexagonal Direction
#pragma GCC target ("avx2")
#pragma GCC optimization ("O3")
#pragma GCC optimization ("unroll-loops")
#define fast ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL)
#define sp(a , x) cout << fixed << setprecision(a) << x << endl;
#define endl "\n"
#define pb push_back
#define pf push_front
#define ub upper_bound
#define lb lower_bound
#define F first
#define S second
#define mset(a, b) memset(a, b, sizeof a)
#define sz(x) ((int)(x.size()))
#define sqr(x) ((x) * (x))
#define graph vector<int>
#define vi vector<int>
#define vvi vector<vector<int>>
#define pi pair<int,int>
#define all(c)                      c.begin() , c.end()
#define rep(i,a) for(int i=0;i<a;i++)
#define rrep(i,a,b) for(int i=a;i>=b;i--)
#define iter(it,a) for(auto it=a.begin();it!=a.end();it++)
#define PQP priority_queue<pi, vector<pi>, greater<pi>>
#define PQI priority_queue<int, vector<int>, greater<int>>
#define dbg debug
#define inf (int)1e18
const long double EPS = 0.0000000001;
const long double PI = 3.1415926535897932384;
//vec.resize(unique(all(vec)) - vec.begin());
 int dy[4] = {0,0,1,-1}, dx[4] = {1,-1,0,0};

 // Template Ends Here.

  /// define some data....... |
 const int N = 30001;

 int dp[N];
 map<int, int> mp;

 int f(int pre, int cur){

     if(cur >= N || cur < 0)
         return 0;
     int &ret = dp[cur];
     if(ret != -1)
         return ret;

     ret = 0;
     int l = cur - pre;
     int op1 = 0, op2 = 0, op3 = 0;

      if(mp.count(cur+l-1)){

          op1 = mp[cur+l-1] + f(cur, cur + l - 1);
      }
      op1 = max(op1, f(cur, cur + l - 1));

       if(mp.count(cur+l)){

          op2 = mp[cur+l] + f(cur, cur + l);
      }
      op2 = max(op2, f(cur, cur + l));

       if(mp.count(cur+l+1)){

          op3 = mp[cur+l+1] + f(cur, cur + l + 1);
      }
      op3 = max(op3, f(cur, cur + l + 1));


      return ret = max({op1, op2, op3});
 }

 void solve()
 {
     int n, d;
     cin >> n >> d;
     rep(i,n){
         int x;
         cin >> x;
         mp[x]++;
     }
     mset(dp, -1);

     int ans = f(0, d);
     if(mp.count(d))
         ans++;
     cout << ans << "\n";
 }

int32_t main(){
    fast;
    int test = 1;
    // cin >> test;
    int tc = 1;
    while (test--)
    {
        solve();
    }
}