#include <iostream>
#include <queue>
 
using namespace std;
 
int main() {
    int n;
    cin >> n;
    int A[n--];
    for (int i = 0; i <= n; i++) {
        cin >> A[i];
    }
    priority_queue<int> pq;
    pq.push(A[0]);
    int ans = 0;
    int it = 0;
    while (it < n && !pq.empty()) {
        int x = pq.top();
        pq.pop();
        for (int i = 1; i <= x; i++) {
            if ((it + i) <= n) {
                pq.push(A[it+i]);
            } else {
                break;
            }
        }
        it += x;
        ans++;
    }
    if (it < n) {
        cout << "BRAK\n";
    } else {
        cout << ans << endl;
    }
}

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MTAKMiAwIDMgMCAzIDAgMyAwIDAgMQo=

10
2 0 3 0 3 0 3 0 0 1