#include <iostream>

int main()
{
    int n;
    std::cin >> n;
    
    double a[101];
    a[0] = 4.0;
    a[1] = 3.0;
    
    for(int i = 2; i <= n; i++)
    {
        a[i] = (4.75 * a[i - 1]) - (3.0 * a[i - 2]);
    }
    
    std::cout << a[n] << std::endl;
    
    return 0;
}