#include<iostream>
using namespace std;
int main()
{
	int n, a[10001],ans=1,max=1;
	cin >> n;
	for (int i = 1; i <= n; i++)
	{
		cin >> a[i];
		if (a[i] - a[i - 1] == 1)
		{
             ans++;
		}	
		else
		{
			if (ans >= max)
			{
				max = ans;
			}
			ans = 1;
		}
	}
	if (ans >= max)
		max = ans;
	cout << max;
	return 0;
}