#include <bits/stdc++.h>

#define FOR(i, a, n) for(int i = (int)(a); i < (int)(n); ++i)
#define REP(i, n) FOR(i, 0, n)
#define all(a) a.begin(),a.end()
#define pb push_back

typedef unsigned long long llu;
typedef long long ll;
typedef long double ld;

using namespace std;

int main(){
	int n, aux, res = 0;
	scanf("%d", &n);
	vector<int> idx, sum;
	map<int,int> num;
	map<int,int>::iterator it, rit, zit;
	REP(i, n){
		cin >> aux;
		it = num.find(aux);
		if(it == num.end()) num.insert(make_pair(aux,1));
		else it->second++;
	}
	for(it = num.begin(); it != num.end(); it++){
		idx.pb(it->first);
		sum.pb(it->second);
	}
	REP(i, idx.size()){
		int a = 0, b = 0;
		if(i && abs(idx[i]-idx[i-1]) <= 1) a = sum[i-1];
		if(i != idx.size()-1 && abs(idx[i+1]-idx[i]) <= 1) b = sum[i+1];
		res = max(res, (sum[i] + max(a,b)));
	}
	cout << res << endl;
	return 0;
}