Finally passed test case 6 with this, although I'm still not sure why. Is there any way to get a look at the test cases?

int main() { int chapters{0}, problemsPerPage{0}, problemsInChapter{0}, pageNumber{0}, specials{0};

cin >> chapters >> problemsPerPage;

while (cin >> problemsInChapter)
    for (int problemNumber{0};
         problemNumber < problemsInChapter;
         ++problemNumber)
    {
        if (problemNumber % problemsPerPage == 0)
            ++pageNumber;
        if (problemNumber + 1 == pageNumber)
            ++specials;
    }

cout << specials;
return 0;

}