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

using ll = long long;
using pll = pair<ll,ll>;
using vll = vector<ll>;
using vi = vector<int>;
using pi = pair<int, int>;
using vpi = vector<pair<int, int>>;
using vai = vector<array<int, 3>>;

#define x first
#define y second
#define all(x) x.begin(), x.end()

void solve() {
    int n, k; cin >> n >> k;
    int one = 0;
    while (n--) {
        int in; cin >> in;
        if (in == 1) {
            one++;
        }
    }

    ll ans = 0;
    for (int i = 0; i < one; i++) {
        ans += max(0, one-i-k+1);
    } cout << ans;
}

int main() {
	ios::sync_with_stdio(0);
    cin.tie(0);

    int t=1;
    //cin >> t;
    while (t--) {
        solve();
    }
}