View Compilation Error

0_0_14574468_10893.cpp: In member function 'void Segment_Tree::update(int, int, int, int, int)':
0_0_14574468_10893.cpp:24:52: error: 'sqrt' was not declared in this scope
   if (l == r){ node[rt] = (LL)sqrt((double)node[rt]); return; }
                                                    ^