#include<iostream>
using namespace std;
int main()
{
	int n;
	cin>>n;
	int numbers[n+1] ={},t,max=0;
	for(int i = 0;i<n;i++){
		cin>>t;
		numbers[t]++;
	}
	
	for(int i = 0;i<n;i++){
		if(max< numbers[i] + numbers[i+1])
		max = numbers[i] + numbers[i+1];
	}
	cout<<max;
	
}