#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;
}
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