//nunta
#include<fstream.h>


int main()
{long int s,n,l,fact,j,nr,i;
ifstream f("nunta.in");
ofstream g("nunta.out");
f>>n;  nr=1;  fact=1;
for(i=1;i<=n/2;i++)
	{l=n-i;
	fact*=i;
	s=1;
	for(j=l;j>l-i;--j)
		s*=j;
	s/=fact;
	nr+=s;
       }
g<<nr;
f.close();
g.close();
return 0;
}