#include <stdio.h>
#include <stdlib.h>

#define DEBUG 0

int main ( int argc , char * argv[] ) {

    int n;
    int array[31];

    array[0] = 1;
    array[1] = 0;
    array[2] = 3;
    array[3] = 0;

    int i = 0;
    for ( i = 4 ; i < 31 ; i++ ) {
        array[i] = array[i-2] * 4 - array[i-4];
    }

    while ( 1 ) {
        scanf("%d" , &n);

        if ( n == -1 )
            break;

        printf("%d\n" , array[n]);
    }

    return 0;
}