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

int main() {
    int n, k;
    cin >> n >> k;

    vector<int> retek (n, 0);
    long long db = 0;

    for (int i = 0; i < n; i++) {
        cin >> retek[i];
        if (retek[i] == 1) db++;
    }

    if (db < k) {
        cout << 0;
        return 0;
    }

    long long m = db - k + 1;
    long long utvonalak = m * (m + 1) / 2;

    cout << utvonalak;

    return 0;
}