#include <iostream>
#include <vector>

using namespace std;


int main()
{
	int n, k, count = 0;
	cin >> n >> k;
	for (int i = 0; i < n; i++)
	{
		int x;
		cin >> x;
		if (x == 1)
		{
			count++;
		}
	}

	long long ans = 0;

	for (int i = 0; i < count; i++)
	{
		if (count - i + 1 < k)
		{
			break;
		}
		ans += max(0, count - i - k + 1);
	}
	cout << ans;
}