AC

//涂色问题
#include<bits/stdc++.h>
using namespace std;
int main(){
long long n,a[110] = {0,3,6,6};
cin>>n;
for(long long i=4;i<=n;i++){
a[i]=a[i-1]+2*a[i-2];
}
cout<<a[n];

return 0;

}