#include <iostream>
#include <algorithm>
using namespace std;

int main()
{
    int n;
    cin >> n;
    int a[n];
    int i;
    for (i=0; i < n; i++)
    {
        cin >> a[i];
    }
    sort (a, a+n);
    int m=0, x=0, p;
    for (i=0; i < n; i++)
    {
        if (x==0)
        {
            if (a[i]== a[i+1] || a[i+1] - a[i] == 1)
            {
                p= a[i];
                x=2;
            }
        }
        else
        {
            if (a[i+1]== p || a[i+1]== p+1)
            {
                x++;
            }
            else
            {
                m= max(m, x);
                x=0;
            }
    }

}
cout << m << endl;
return 0;
}