#include <iostream>


int pell(int n)
{
    int n2 = 2, n1 = 2;

    for(int i=0;i<n;i++)
    {
        n1 = n2;
        n2 = n1 * 2 + n2;

    }
    return n2;


}
int main()
{
    int n = 10;
    pell(10);

    std::cout << pell(10) << " " << std::endl;

    return 0;
}