View Compilation Error

0_0_31933146_17609.cpp: In function 'long long int fanfa2(long long int)':
0_0_31933146_17609.cpp:15:47: error: 'f2' was not declared in this scope
  return (18*(n/2)%mod*(n/2)%mod*a%mod+7*f2(n/2)%mod)%mod;
                                               ^
0_0_31933146_17609.cpp: In function 'int main()':
0_0_31933146_17609.cpp:22:8: error: 'n' was not declared in this scope
   cin>>n>>a>>b;
        ^