#include <stdio.h>
#include <iostream>
#include <stdlib.h>
#include <string>
#include <string.h>
#include <vector>
#include <stack>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <assert.h>
#include <algorithm>
#include <iomanip>
#include <time.h>
#include <math.h>
#include <bitset>

#pragma comment(linker, "/STACK:256000000")

using namespace std;

typedef long long int int64;
typedef long double double80;

const int INF = (1 << 29) + 5;
const int64 LLINF = (1ll << 59) + 5;
const int MOD = 1000 * 1000 * 1000 + 7;

int n;
map<int, int> arr;


int main()
{
	//freopen("input.txt", "r", stdin);
	//freopen("output.txt", "w", stdout);

	scanf("%d", &n);
	int v;
	for (int i = 0; i < n; ++i)
	{
		scanf("%d", &v);
		++arr[v];
	}

	int ans = 0;
	for (auto it = arr.begin(); it != arr.end(); ++it)
	{
		auto gg = it;
		++gg;
		if (gg!=arr.end() &&gg->first == it->first + 1)
			ans = max(ans, it->second + gg->second);
		else
			ans = max(ans, it->second);
	}

	cout << ans;
	fclose(stdin);
	fclose(stdout);

	return 0;
}