#include <bits/stdc++.h>

using namespace std;

int main()
{
    int n, k;
    cin >> n >> k;
    int count = 0;
    for (int i = 0; i < n; i++) {
        bool next;
        cin >> next;
        count += next;
    }

    long long ans = 0;
    long long num = count - k + 1;
    if (num > 0) {
        ans = (num)*(num+1) / 2;
    }

    cout << ans << endl;

    return 0;
}