View Compilation Error

0_0_32656668_6411.cpp: In function 'int main()':
0_0_32656668_6411.cpp:12:44: error: 'sqrt' was not declared in this scope
             if ((n * n + sqrt(n * n - 4 * m)) / 2.0 == (int)(n * n + sqrt(n * n - 4 * m)) / 2.0)
                                            ^