#include <iostream>

using namespace std;
typedef long long ll;

ll N, K, V, a, r;

int main()
{
    cin >> N >> K;
    for (ll n = 0; n < N; n++) {
        cin >> a;
        V += a == 1;
    }
    for (ll i = 0; i < V-K+1; i++) {
        r += V - K - i + 1;
    }
    cout << r << endl;
}