#include<iostream>
#include<map>
using namespace std;

int main()
{
	int n;
	cin>>n;
	
	int A[n];
	
	for(int i=0;i<n;i++)
	cin>>A[i];
	
	map<int,int> mp;
	
	for(int i=0;i<n;i++)
	{
		if(mp.find(A[i])==mp.end())
		mp[A[i]]=1;
		else
		mp[A[i]]++;
	}
	map<int,int>::iterator it;
	
	it = mp.begin();
	int a = (it)->first;
	int b = (it)->second;
	int count=0,m=b;
	it++;
	for(;it!=mp.end();it++)
	{
		int c = (it)->first;
		int d = (it)->second;
		m = max(m,d);
		if((c-a)<=1)
		{
			count = max(count,b+d);
			a = c;
			b = d;
		}
		a = c;
		b = d;
	}
	
	if(count!=0 && count>=m)
	cout<<count<<endl;
	else
	cout<<m<<endl;
	
	return 0;
}