/in/foo.cc: In function 'int judge(double, double)':
/in/foo.cc:9:19: error: 'floor' was not declared in this scope
  if (a1 - floor(a1) < 0.00000001)
                   ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:20:33: error: 'sqrt' was not declared in this scope
  for (int k = 1; k < (sqrt(1+8*M)-3)/2; k++) {
                                 ^