/in/foo.cc: In function 'int main()':
/in/foo.cc:9:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(long long i=0;i<s[u].size();i++){
                     ~^~~~~~~~~~~~
/in/foo.cc:28:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(long long j=0;j<s[i].size();j++){
                     ~^~~~~~~~~~~~