#include<bits/stdc++.h>
using namespace std;
int main()
{
	int n,a[101]={0},i,temp;
	cin>>n;
	for(i=0;i<n;i++)
	{
		cin>>temp;
		a[temp]++;
	}
	int mx=INT_MIN;
	for(i=1;i<100;i++)
	{
		int curr1=a[i],curr2=a[i],curr;
		if(a[i-1]!=0)
			curr1+=a[i-1];
		if(a[i+1]!=0)
			curr2+=a[i+1];
		curr=max(curr1,curr2);
		if(curr>mx)
			mx=curr;
	}
	cout<<mx<<endl;
	return 0;
}