View Compilation Error

0_0_29973172_10062.cpp: In function 'll mul(ll, ll, ll)':
0_0_29973172_10062.cpp:36:10: error: '_int128' was not declared in this scope
  return (_int128)a*b%n;
          ^
0_0_29973172_10062.cpp:36:18: error: expected ';' before 'a'
  return (_int128)a*b%n;
                  ^