private int start(int i) {
        int first = this.firstNonEmptyBucket();
        if(i < first) {
            return -1;
        } else if(i == first) {
            return 0;
        }
        int result = 0;
        for(int j = first; j < i; j++) {
            if(buckets[j] != null) {
                result += buckets[j].size();
            }
        }
        return result;
    }