View Compilation Error

0_0_25976155_21524.cpp: In member function 'bool point::operator<(const point&) const':
0_0_25976155_21524.cpp:18:18: error: passing 'const point' as 'this' argument of 'long long int point::operator*(const point&)' discards qualifiers [-fpermissive]
   return (*this)*b>0;
                  ^