View Compilation Error

0_0_37847987_30873.cpp: In function 'void solve()':
0_0_37847987_30873.cpp:453:55: error: 'gcd' was not declared in this scope
             ans = (ans + qpow(m, d - 1) * gcd(i / d, m) % MOD * phi[i/d] % MOD);
                                                       ^