how the scanf() is executing before printf()

I have the following code to just implement the pow() as in math.h library. Well I have two questions:

1. Why the scanf() statement is taking input before it prints "power:" from the printf() function?

2. How can I calculate the power of big integers, like suppose the power calculated is like : 22235645654789787978797797 (just for example). How do I calculate and print it.
   
   

   #include <stdio.h>
   unsigned long long int pow(unsigned long long int n,unsigned long long int d);
   int main(){
   
   unsigned long long int a,x,n;
   printf("Number:");
   scanf("%un",&a);
   printf("power:");
   scanf("%un",&n);
   x = pow(n,a);
   printf("%un",x);
   }
   unsigned long long int pow(unsigned long long int n,unsigned long long int d){
   if(n+1==1)
       return 1;
   return d*pow(n-1,d);
   }
   

In the image you can see the input of variable n is taking input before printing "power:" from printf(), so no matter what input do you type.

Please help me understand it. Open for any suggestions and comments.