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

void back(int k)
{if(k==n) nr++;
else if(k<n){ back(k+1); back(k+2);}

}

int main()
{ifstream f("nunta.in");
ofstream g("nunta.out");
f>>n;
    back(0);
g<<nr;
f.close();   
g.close();   
return 0;   
}