#include <bits/stdc++.h>

using namespace std;

int main()
{
    int ret, k, ossz = 0,szamlalo = 0;
    cin >> ret >> k;
    //vector<int> retek(ret);
    int n;
    for (int i = 0; i < ret; i++) {
        cin >> n;
        if (n == 1) {
            szamlalo += 1;
        }
    }
    for (int i = 1; i <= szamlalo; i++) {
        ossz += max(0,szamlalo-i-k+2);
    }
    cout << ossz << endl;
    return 0;
}