/in/foo.cc: In function 'int main()':
/in/foo.cc:31:51: warning: format '%d' expects argument of type 'int', but argument 2 has type 'std::stack<char>::size_type {aka long unsigned int}' [-Wformat=]
   printf("%d\n", a.size() / 4 + (a.size() / 2 % 2));
                                                   ^