/in/foo.cc: In function 'void dfs3(int, int, int, int)':
/in/foo.cc:43:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i = 0; i < ch[now].size(); i++) {
                 ~~^~~~~~~~~~~~~~~~
/in/foo.cc: In function 'void build_ST(int)':
/in/foo.cc:55:48: warning: suggest parentheses around '-' inside '<<' [-Wparentheses]
    st[j][i] = max(st[j][i - 1], st[j + (1 << i - 1)][i - 1]); 
                                              ~~^~~