View Compilation Error

0_0_39506029_12420.cpp: In function 'int main()':
0_0_39506029_12420.cpp:38:47: error: 'sqrt' was not declared in this scope; did you mean 'st'?
   38 |                 int st=min((ll)b.size()-1,(ll)sqrt(b.size()));
      |                                               ^~~~
      |                                               st