What could be its o/p and Why?

‪#‎include‬<stdio.h>
void fun(int);
typedef int (*pf) (int, int);
int proc(pf, int, int);
int main(){
    int a=3;
    fun(a);
    return 0;
}
void fun(int n){
    if(n > 0){
    fun(--n);
    printf("%d,", n);
    fun(--n);
}
}