#include<iostream>
#include<cmath>
#include<algorithm>
using namespace std;
int main()
{
	int n;
	cin >> n;
	long long * p = new long long[n];
	for (int i = 0; i < n; i++)
	{
		cin >> p[i];
	}
	int count = 1, cmax = 1;
	for (int i = 1; i < n; i++)
	{
		if (p[i] == p[i - 1] + 1)
		{
			count++;
			
		}
		else
		{
			cmax = count;
			count = 1;
		}

	}
	if (count > cmax)
		cout << count;
	else
		cout << cmax;
	return 0;
}