View Code of Problem 3692

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