View Code of Problem 3834

#include<stdio.h>

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