/in/foo.cc: In function 'bool check(int)':
/in/foo.cc:28:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=0;i<G[u].size();i++)
               ~^~~~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:47:9: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
    mid=l+r>>1;
        ~^~
/in/foo.cc:62:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for(int i=0;i<G[u].size();i++)
                ~^~~~~~~~~~~~