View Compilation Error

0_0_30763446_12168.cpp: In function 'void dfs(int, int, int)':
0_0_30763446_12168.cpp:38:43: error: 'qpow' was not declared in this scope
                 ans*=qpow(2,y+1-grade[cur])-1+mod;
                                           ^
0_0_30763446_12168.cpp: In function 'int main()':
0_0_30763446_12168.cpp:65:18: error: 'qpow' was not declared in this scope
     ans*=qpow(2,m);
                  ^