View Code of Problem 3692

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
using namespace std;
int main(void)
{
    int n;
    long long num[51] = {0};
    num[0] = 0;
    num[1] = 3;
    num[2] = 6;
    num[3] = 6;
    for (int i = 4; i < 51;i++){
        num[i] = num[i - 1] + 2 * num[i - 2];
    }
    while (cin >> n)
        cout << num[n] << endl;
}