/in/foo.cc: In function 'int main()':
/in/foo.cc:7:17: error: unable to find numeric literal operator 'operator""n'
  cout<<n*(n+1)*(2n+1)/6<<endl;
                 ^~
/in/foo.cc:7:17: note: use -std=gnu++11 or -fext-numeric-literals to enable more built-in suffixes