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

int main()
{
	size_t n;
	cin >> n;
	vector<short> arr(n);
	size_t i;
	for (unsigned short i = 0; i < n; ++i)cin >> arr[i];
	map<unsigned short, size_t>mymap;
	for (i = 0; i < n; ++i)
	{
		mymap[arr[i]]++;
	}
	size_t best(0), thissum;
	map<unsigned short, size_t>::iterator itr=mymap.begin();
	while(next(itr)!=mymap.end())
	{
		thissum = itr->second;
		if (itr->first - (next(itr))->first == -1)	thissum += next(itr)->second;
		if (thissum > best)best = thissum;
		++itr;
	}
	if (itr->second > best)cout<<itr->second<<endl;
	else cout << best << endl;
    return 0;
}