/in/foo.cc: In function 'void dfs(long long int)':
/in/foo.cc:48:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (ll i=0;i<G[x].size();++i){
                 ~^~~~~~~~~~~~
/in/foo.cc: In function 'void dfs_cover(long long int)':
/in/foo.cc:60:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (ll i=0;i<G[x].size();++i){
                 ~^~~~~~~~~~~~
/in/foo.cc: In function 'bool check(long long int)':
/in/foo.cc:90:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (ll i=0;i<G[1].size();++i){
                 ~^~~~~~~~~~~~