#include<bits/stdc++.h>
using namespace std;
int main(){
	int n,a,m = 1,minn = INT_MIN,x = -11;
	cin >> n;
	for(int i = 1 ; i <= n ; i++)
	{
		cin >> a;
		
		if(a - x == 1)
		{
			m += 1;
			if(m > minn)
			{
				minn = m;
			} 
		}
		else
		{
			m = 1;
		
		}
		x = a;
	}
	cout << minn;
	return 0;
}}