View Code of Problem 3834

#include<stdio.h>
int main(){
	int n,i;
	while(scanf("%d",&n)!=EOF){
	long long int a[30]={0,2,5};
	for(i=3;i<=n;i++){
		a[i]=a[i-1]*3-1;
	}
	printf("%lld\n",a[n]);
}
}