#include <list>
#include <iostream>
#include <vector>
#include <bitset>
#include <algorithm>

using namespace std;

int main() {

    int n, k;
    cin >> n >> k;

    int true_fields = 0;
    int sol = 0;
    for (int i = 0; i < n; i++) {
        bool field;
        cin >> field;

        if (field) {
            true_fields++;
            if (true_fields >= k) sol += true_fields - k + 1;
        }
    }

    cout << sol;

    return 0;
}