#include <iostream>
#include <vector>

using namespace std;

int main()
{
    int n, k;
    cin >> n >> k;
    
    int x, egyes = 0; // Initialize egyes to 0
    for(int i = 0; i < n; i++){
        cin >> x;
        if(x == 1){ // Count only the number of 1's
            egyes++;
        }
    }
    
    // If there are not enough 1's to form a group of size k, the result is 0
    if (egyes < k) {
        cout << 0;
        return 0;
    }

    // Calculate the number of ways to choose k 1's from the total number of 1's
    int ossz = 0;
    // The number of ways to choose k 1's from egyes 1's is given by:
    // (egyes - k + 1) * (egyes - k) / 2
    ossz = (egyes - k + 1) * (egyes - k) / 2;

    cout << ossz;
    return 0;
}