POJ 3250 Bad Hair day monotonic stack

Maintaining a monotonically decreasing stack every time the home enters the top of the stack the cow must be seen by the cows inside the other stacks

#include <cstdio>
#include <cstring>
using namespace std;
const int MAXN = 80010;
typedef unsigned long long LL;
int A[MAXN], S[MAXN];
int main ()
{
	int n;
	scanf ("%d", &n);
	for (int i = 1; I <= n; i++)
		scanf ("%d", &a[i]);
	int top = 0;
	LL ans = 0;
	for (int i = 1, i <= N; i++)
	{while
		(top && a[i] >= A[s[top]])
			top--;
		Ans + = top;
		S[++top] = i;
	}	
	printf ("%llu\n", ans);
	return 0;
}