#include<bits/stdc++.h>
using namespace std;
int A[100];
int main()
{
    int a,b,s,c;
    cin>>a;
    memset(A,0,400);
    for(b=0;b<a;b++)
    {
        cin>>c;
        A[c]++;
    }int max=0;
    for(b=0;b<a-1;b++)
    {
        s=A[b]+A[b+1];
        if(s>max)
            max=s;
    }
    cout<<max;
}