/in/foo.cc: In function 'int main()':
/in/foo.cc:15:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         while(flag<Prime.size()&&i*Prime[flag]<=n)
               ~~~~^~~~~~~~~~~~~
/in/foo.cc:23:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0;i<v.size();i++)
                 ~^~~~~~~~~