void main()
{
    int k = 9; // 9 code
    int n = 60; // 60 student

    int p = 1;
    int q = 2;

    int locA = p * 2 + q - 1; // location of A
    int locB = (locA > k ? locA - k : (locA + k > n ? locA + k : -1)); // location of B, -1 if invalid
    if (locB == -1) { cout << "Location not found (-1)" << endl; return; }

    int code = (locA > k ? locA % k : locA); // B need to match this code

    cout << "Code needed to be matched: " << code << endl;

    int v = locB % 2 + 1;
    int u = (locB - v) / 2;

    cout << "B is need to be at row: " << u << "  position: " << v << endl;

}