/*
Solved By : Kazi Mahbubur Rahman (cryptic.coder)
Time :
Rank :
Complexity:
*/

#define _CRT_SECURE_NO_WARNINGS

#include <set>
#include <map>
#include <list>
#include <cmath>
#include <ctime>
#include <queue>
#include <stack>
#include <cctype>
#include <cstdio>
#include <string>
#include <vector>
#include <cassert>
#include <cstdlib>
#include <cstring>
#include <sstream>
#include <iostream>
#include <algorithm>

using namespace std;

#define FOR(i, L, U) for(int i=(int)L; i<=(int)U; i++)
#define FORD(i, U, L) for(int i=(int)U; i>=(int)L; i--)

#define READ(x) freopen(x, "r", stdin)
#define WRITE(x) freopen(x, "w", stdout)

#define ff first
#define ss second
#define PQ priority_queue
#define PB push_back
#define SZ size()

#define EPS 		1e-9
#define SQR(x) 		((x)*(x))
#define INF 		2000000000
#define TO_DEG 		57.29577951
#define PI 			2*acos(0.0)

#define ALL_BITS					((1 << 31) - 1)
#define NEG_BITS(mask)				(mask ^= ALL_BITS)
#define TEST_BIT(mask, i)			(mask & (1 << i))
#define ON_BIT(mask, i)				(mask |= (1 << i))
#define OFF_BIT(mask, i)			(mask &= NEG_BITS(1 << i))
#define IS_POWER_TWO(x)				(x && !(x & (x-1)))
#define OFF_RIGHTMOST_SET_BIT(x)	(x & (x-1))

typedef long long LL;
typedef unsigned long long ULL;
typedef pair<int, int> PII;
typedef pair<double, double> PDD;
typedef vector<bool> VB;
typedef vector<int> VI;
typedef vector<double> VD;
typedef vector<char> VC;
typedef vector<string> VS;
typedef map<int, int> MII;
typedef map<char, int> MCI;
typedef map<string, int> MSI;
typedef vector<vector<bool> > VVB;
typedef vector<vector<int> > VVI;
typedef vector<vector<double> > VVD;
typedef vector<vector<PII> > VVPII;

int GCD(int a, int b) { while (b)b ^= a ^= b ^= a %= b;  return a; }

// UP, RIGHT, DOWN, LEFT, UPPER-RIGHT, LOWER-RIGHT, LOWER-LEFT, UPPER-LEFT
int dx[8] = { -1, 0, 1, 0, -1, 1,  1, -1 };
int dy[8] = { 0, 1, 0,-1,  1, 1, -1, -1 };

// Represents all moves of a knight in a chessboard
int dxKnightMove[8] = { -1, -2, -2, -1,  1,  2, 2, 1 };
int dyKnightMove[8] = { 2,  1, -1, -2, -2, -1, 1, 2 };

inline int src() { int ret; scanf("%d", &ret); return ret; }

#define WHITE 0
#define GRAY 1
#define BLACK 2

#define MAX 107

int N;
int arr[MAX];
int f[MAX];

int main()
{
	//READ("input.txt");
	//WRITE("output.txt");
	int i, j, k;
	int TC, tc;
	double cl = clock();

	cin >> N;
	FOR(i, 0, N - 1) {
		cin >> arr[i];
		f[arr[i]]++;
	}

	int ans = 0;
	for (int i = 0; i < 99; i++) {
		if (f[i] >= 2) ans = max(ans, f[i]);
		if (f[i + 1] >= 2) ans = max(ans, f[i+1]);
		if (f[i] && f[i + 1]) {
			ans = max(ans, f[i] + f[i + 1]);
		}
	}

	cout << ans << endl;

	cl = clock() - cl;
	fprintf(stderr, "Total Execution Time = %lf seconds\n", cl / CLOCKS_PER_SEC);

	return 0;
}