Critical Mass uva 580

#include<iostream>
#include<cstring>
#include<algorithm>
#include<set>
using namespace std;

 int f[44],n;

 signed main() {
	int i; 
	f[3]=1,f[4]=3;
	for(i=5;i<=30;i++){
		f[i] = f[i-1]*2+ (1<<(i-4)) - f[i-4];
	}
	int x;
	while(cin>>x,x){cout<<f[x]<<endl;}
 }