#include <iostream>

#define forn(i,n) for (int i = 0; i < n; i++)

using namespace std;

void swap (int *p1, int *p2)
{
    int temp = *p1;
    *p1 = *p2;
    *p2 = temp;
}

int main()
{
    int n,a[100];
    cin>>n;
    forn(i,n)
    {
        cin>>a[i];
    }
    for (int i = n-1; i > 0; i--)
        for (int j = 0; j < i; j++)
        {
            if (a[j] > a[j+1])
                swap(a[j],a[j+1]);
        }
    int max = 0, p1 = 0, p2 = 0,i = 0;
    while (i < n)
    {
        int temp = a[i];
        if (p1 == 0)
        {
            while (a[i] - temp == 0)
            {
                i++;
                p1++;
            }
            while (a[i] - temp == 1)
            {
                i++;
                p2++;
            }
        }
        else
        {
            while (a[i] - temp == 0)
            {
                i++;
                p2++;
            }
        }
        if (p1 + p2 > max)
            max = p1 + p2;
        if (a[i] - a[i-1] == 1)
            p1 = p2;
        else
            p1 = 0;
        p2 =  0;
    }
    cout<<max<<endl;
    return 0;
}