/in/foo.cc: In function 'void DFS(int)':
/in/foo.cc:45:26: error: 'k' was not declared in this scope
     for (int i = 1; i <= k; i++)
                          ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:129:5: error: 'k' was not declared in this scope
     k = log2(n);
     ^