//用排列组合去做
include [HTML_REMOVED]
include [HTML_REMOVED]
using namespace std;
int c(int a,int b)
{
int x=a;int y=b;//肯定a大于b
double s,s1,s2;
s1=1;
s2=1;
for(int i=y;i>0;i–)
{
s1=x;
x–;
}
for(;y>0;y–)
{
s2=y;
}
s=s1/s2;
return s;
}
int main(int argc,char*argv[])
{
int a;
double ans=0;
cin>>a;
if(a%2!=0){
for(int p=a+1;a>0;a=a-2)
{
p–;
ans+=c(p,a);
}
}
if(a%2==0)
{
for(int q=a+1;a>0;a=a-2)
{
q–;
ans+=c(q,a);
}
ans++;
}
cout<<ans;
return 0;
}