View Compilation Error

0_0_19287002_13778.cpp: In function 'int main()':
0_0_19287002_13778.cpp:10:12: error: 'f' was not declared in this scope
   cout<<f(n);
            ^
0_0_19287002_13778.cpp: In function 'int main()':
0_0_19287002_13778.cpp:35:5: error: redefinition of 'int main()'
 int main(){  
     ^
0_0_19287002_13778.cpp:3:5: note: 'int main()' previously defined here
 int main()
     ^