#include<bits/stdc++.h>
using namespace std;
#define ll long long int
int main()
{
	ll n;
	cin>>n;
	ll a[n];
	ll b[101];ll i;
	memset(b,0,sizeof(b));
	for(i=0;i<n;i++)
	{
		cin>>a[i];
		b[a[i]]++;
	}
	ll x=2;
	for(i=1;i<=100;i++)
	{
		x=max(x,b[i]+b[i-1]);
	}
	cout<<x<<endl;
}