#include <bits/stdc++.h>

using namespace std;

long long n, a[100005], ship[100005], last[100005], ans;

int main()
{
	scanf("%d", &n);
	for (int i = 1 ; i <= n ; i ++)
	{
		scanf("%d", &a[i]);
	}
	ans = 1;
	ship[ans] = a[2] - a[1];
	last[ans] = a[2];
	for (int i = 3 ; i <= n ; i ++)
	{
		bool flag = false;
		for (int j = 1 ; j <= ans ; j ++)
		{
			if (last[j] + ship[j] == a[i])
			{
				flag = true;
				break;
			}
		}
		if (!flag)
		{
			ans ++;
			ship[ans] = a[i] - a[1];
			last[ans] = a[i];
		}
	}
	printf("%d", ans);
	return 0;
}