View Code of Problem 3692

#include<stdio.h>
#include<string.h>
#include<math.h>

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

	
	return 0;
}