UVA 580(p331)----Critical Mass

#include<iostream>
#include<cstdio>
#include<cmath>
using namespace std;
const int maxn=30+5;
int f[maxn],g[maxn];
void prepare()
{
f[0]=0;f[1]=0;
f[2]=0;f[3]=1;
g[0]=1;g[1]=2;
g[2]=4;g[3]=7;
for(int i=3;i<=30;i++)
{
int tmp=0;
for(int k=2;k<=i-2;k++)
tmp+=g[k-2]*pow(2,i-k-2);
f[i]=pow(2,i-3)+tmp;
g[i]=pow(2,i)-f[i];
}
}
int main()
{
int n;
prepare();
while(scanf("%d",&n)==1&&n)
printf("%d\n",f
);
return 0;
}