//nunta   
#include<fstream.h>   
long int nr,n;

void back(long int s)
{if(s==n) nr++;
back(s+1);
back(s+2);
}  
  
int main()   
{//long int s,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;   
}