View Code of Problem 3692

#include<bits/stdc++.h>
using namespace std;
 
long long a[51];
int main()
{
    a[1] = 3;
    a[2] = 6;
    a[3] = 6;
    int n;
    while (cin >> n)
    {
        for (int i = 4; i <= n; i++)
        {
            a[i] = a[i - 1] + a[i - 2] * 2;
        }
        cout << a[n] << endl;
    }
}