#include <bits/stdc++.h>
using namespace std;

int N, K, M, result;
int main() {
    cin >> N >> K;

    while (N--) {
        char c;
        cin >> c;
        M += c == '1';
    }

    if (M < K) {
        cout << 0 << '\n';
        exit(0);
    }
    
    for (int i = 0; i < M - K + 1; i++) {
        result += M - i - K + 1;
    }
    
    cout << result;
}