View Compilation Error

0_0_20759463_26274.cpp: In function 'LL Lucas(LL, LL, LL)':
0_0_20759463_26274.cpp:40:63: error: 'modpow' was not declared in this scope
         ret = (ret * fac[a] * modpow(fac[b]*fac[a-b]%p, p-2, p)) % p;
                                                               ^