View Compilation Error

0_0_38587316_14694.cpp: In function 'int f(int)':
0_0_38587316_14694.cpp:7:23: error: 'sqrt' was not declared in this scope
  for (int i = 2; i <= sqrt(p); i++)
                       ^~~~
0_0_38587316_14694.cpp:7:23: note: suggested alternative: 'qsort'
  for (int i = 2; i <= sqrt(p); i++)
                       ^~~~
                       qsort