#include <bits/stdc++.h>
using namespace std;
int b[10005];
int main()
{
	int n,a[10005],m = 0;
	cin >> n;
	for (int i = 0;i < n;i ++)
	{
		cin >> a[i];
	}
	for (int i = 1;i < n;i ++)
	{
		if (a[i] - a[i - 1] == 1)
		{
			b[m] ++;
		}
		else
		{
			m ++;
		}
	}
	sort(b,b + m);
	cout << b[m] + 1 << endl;
	return 0;
}