#include <iostream>
#include <algorithm>
using namespace std;

int main() {
	long long n, k, f = 0, routes = 0;
	cin >> n >> k;
	for (int i = 0; i < n; i++) {
		int b;
		cin >> b;
		if (b) f++;
	}
	for (int i = 1; i <= f; i++) {
		routes += max((long long)0, f - i - k + 2);
	}
	cout << routes;
	return 0;
}