/in/foo.cc: In function 'void dfs(int)':
/in/foo.cc:24:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for (int j = 0; j < m[i].size(); j++)
                    ~~^~~~~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:67:6: warning: unused variable 'z' [-Wunused-variable]
  int z;
      ^