#include<stdio.h>
_int64 a[41]={3,8};
int main()
{
int n,i;
for(i=2;i<=40;i++)
a[i]=(a[i-1]+a[i-2])*2;
while(scanf("%d",&n)!=EOF)
{
printf("%I64d\n",a[n-1]);
}
return 0;
}
_int64 a[41]={3,8};
int main()
{
int n,i;
for(i=2;i<=40;i++)
a[i]=(a[i-1]+a[i-2])*2;
while(scanf("%d",&n)!=EOF)
{
printf("%I64d\n",a[n-1]);
}
return 0;
}