#include <iostream>
#include <algorithm>
#include <vector>
#include <limits.h>
#include <math.h>

using namespace std;
#define rep(i, n) for ((i) = 0; (i) < (n); (i)++)
#define ran(i, m, n) for ((i) = (m); (i) < (n); (i)++)

int main(int argc, char *argv[])
{
	int n;
	int i;
	static int a[100];
	cin >> n;
	rep (i, 100)
		a[i] = 0;
	rep (i, n) {
		int j;
		cin >> j; a[j]++;
	}
	int ans = 0;
	ran (i, 1, n) {
		int s = a[i-1] + a[i];
		ans = max(s, ans);
	}
	cout << ans << endl;
	return 0;
}