View Compilation Error

0_0_34251777_32617.cpp: In function 'll work(ll)':
0_0_34251777_32617.cpp:16:28: error: 'sqrt' was not declared in this scope
  for (int i = 2; i < sqrt(n); i++)
                            ^
0_0_34251777_32617.cpp:21:17: error: 'sqrt' was not declared in this scope
  ll tmp = sqrt(n);
                 ^