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

int main(int argc, char** argv) 
{
	int count[100];

	for (int i = 0; i < 100; ++i)
	{
		count[i]=0;
	}
	int n;
	cin>>n;
	//int ar[n];
	for (int i = 0; i < n; ++i)
	{
		int x;
		cin>>x;
		count[x]++;
	}

	int max=2;
	for (int i = 1; i < 100; ++i)
	{
		if(count[i-1]+count[i]>max)
			max=count[i-1]+count[i];
	}
	cout<<max<<endl;
	return 0;
}