#include<iostream>
using namespace std;
void ff(int a[1000], int n)
{
        for (int i = 0; i < n; i++)
	{
	for (int j =0; j < n-i-1; j++)
	{
		if (a[j] > a[j + 1])
		swap(a[j], a[j + 1]);
        }
	}
}
int main()
{
	int a[1000];
	int n, c = 1;
	cin >> n;
	for (int i = 0; i < n; i++)
	{
		cin >> a[i];
	}
	ff(a, n);
	int min = 0;
	int m=0;
           for (int i = m; i < n-1; i++)
	{
		c = 1;
	   for (int j = i; j < n-1; j++)
	{
	   if (a[j] + 1 != a[j + 1])
	{
               m = j + 1;
	       break;
			}	
	else
	c++;
		}
	if (min < c)
         min = c;
	}
	cout << min;
	return 0;
}