/*#include <bits/stdc++.h>

 #define LL long long

 using namespace std;

 inline int ra()

 {

     int x=0,f=1; char ch=getchar();

     while (ch<'0' || ch>'9') {if (ch=='-') f=-1; ch=getchar();}

     while (ch>='0' && ch<='9') {x=x*10+ch-'0'; ch=getchar();}

     return x*f;

 }

 int n,s,tot[30005],f[30005],ans;

 bool can[30005][605];

 const int T=300;

 int main()

 {

     n=ra(); s=ra(); can[0][T]=1;

     for (int i=1; i<=n; i++) tot[ra()]++;

     f[0]=tot[0];

     for (int i=0; i<=30000; i++)

     {

         for (int j=-300; j<=300; j++)

         {

             if (s+j<=0) continue;

             if (can[i][j+T] && s+i+j<=30000)

             {

                 f[s+i+j]=max(f[i+j+s],f[i]+tot[s+i+j]);

                 can[i+j+s][j+T]=1;

                 can[i+j+s][j+1+T]=1;

                 can[i+j+s][j-1+T]=1;

             }

         }

         ans=max(ans,f[i]);

     }

     cout<<ans;

     return 0;

 }*/

 #include <bits/stdc++.h>

 #define LL long long

 using namespace std;

 inline int ra()

 {

     int x=,f=; char ch=getchar();

     while (ch<'' || ch>'') {if (ch=='-') f=-; ch=getchar();}

     while (ch>='' && ch<='') {x=x*+ch-''; ch=getchar();}

     return x*f;

 }

 const int T=;

 int n,s,ans;

 int tot[],f[][];

 int main()

 {

     memset(f,-,sizeof(f));

     n=ra(); s=ra();

     for (int i=; i<=n; i++) tot[ra()]++;

     f[s][T/]=;

     for (int i=s; i<=; i++)

         for (int j=; j<=T; j++)

         {

             int t=j-T/+s;

             if (i-t>= && t>)

             {

                 if (f[i-t][j-]!=-) f[i][j]=max(f[i][j],f[i-t][j-]);

                 if (f[i-t][j]!=-) f[i][j]=max(f[i][j],f[i-t][j]);

                 if (f[i-t][j+]!=-) f[i][j]=max(f[i][j],f[i-t][j+]);

                 if (f[i][j]!=-) f[i][j]+=tot[i];

                 ans=max(f[i][j],ans);

             }

         }

         cout<<ans;

         return ;

 }