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

int main() {
    int N, K;
    cin >> N >> K;
    vector<int> retek;
    int ossz = 0;
    int utvonalak = 0;
    retek.push_back(0);

    for (int i = 1; i <= N; i++) {
        int a;
        cin >> a;
        retek.push_back(a);
    }

    int egy = 0;
    int j = 0;
    for (int i = 1; i <= N; i++) {
        if (retek[i] == 1) {
            egy++;
            if (egy >= K) {
                j++;
                utvonalak += j;
            }
        }
    }

    cout << utvonalak;

    return 0;
}