/in/foo.cc: In function 'int main()':
/in/foo.cc:9:25: error: unable to find numeric literal operator 'operator""n'
  cout << n * (n + 1) * (2n + 1) / 6;
                         ^~
/in/foo.cc:9:25: note: use -std=gnu++11 or -fext-numeric-literals to enable more built-in suffixes