#include <stdio.h>
int rec(int n);

int main(void) {
    printf("%d\n", rec(4));
    return 0;
}

int rec(int n) {
    if (n == 1) {return ( 2 );
}
    else if (n == 2) { return ( 1 ); }
    else { return rec(n-1)+2*rec(n-2); }
}