#include<bits/stdc++.h>
using namespace std;//
int n,a[100005],ans=0;
struct lyf{
	int m;
	int r;
	lyf(int x,int y)
	{
		m=x;
		r=y;
	}
};
deque<lyf> q;
int main(){
	cin>>n;
	for(int i=1;i<=n;i++)
	{
		cin>>a[i];
	}
	sort(a+1,a+n+1);
	q.push_front(lyf(a[1],1));
	for(int i=2;i<=n;i++)
	{
		if(!q.empty())
		{
			while(q.front().m<a[i]-1&&!q.empty())
			{
				ans=max(ans,q.front().r);
				q.pop_front();
			}
			if(q.front().m==a[i])
			{
				q.push_front(lyf(a[i],1));
			}
			if(q.front().m==a[i]-1)
			{
				int num=q.front().r;
				q.pop_front();
				q.push_back(lyf(a[i],num+1));
			}
		}
	}
	cout<<ans;
}