View Code of Problem 3692

#define _CRT_SECURE_NO_WARNINGS
#include<bits/stdc++.h>
using namespace std;
long long arr[52];
int main()
{
	arr[0] = 0;
	arr[1] = 3;
	arr[2] = 6;
	arr[3] = 6;
	for (int i = 4; i < 51; i++) {
		arr[i] = arr[i - 1] + 2 * arr[i - 2];
	}
	int n;
	while (cin >> n) {
		printf("%lld\n", arr[n]);
	}

	return 0;
}