View Code of Problem 3692

#include<stdio.h>
int main(){
	long long a[51];
  	a[0]=0;
	a[1]=3;
	a[2]=6;
	a[3]=6;
	for(int i=4;i<=50;i++){
		a[i]=a[i-1]+a[i-2]*2;
	}
	int n;
	while(scanf("%d",&n)!=EOF){
		printf("%lld\n",a[n]);
	}
}