View Compilation Error

0_0_37200653_25945.cpp:1:11: error: '::main' must return 'int'
 void main()
           ^
0_0_37200653_25945.cpp: In function 'int main()':
0_0_37200653_25945.cpp:10:15: error: 'scanf' was not declared in this scope
  scanf("%d",&n);
               ^
0_0_37200653_25945.cpp:15:14: error: 'printf' was not declared in this scope
  printf("2\n");
              ^
0_0_37200653_25945.cpp:17:29: error: 'printf' was not declared in this scope
  printf("%d\n",2*aa[num-1]+2);
                             ^