#include<fstream.h>
int main()
{
	 long n,i,a,b,c;
	 ifstream f("nunta.in");
	 ofstream g("nunta.out");
	 f>>n;a=b=c=1;
	 for(i=1;i<n;i++)
	 { c=a+b; a=b; b=c;}
	 if(n%2==0)g<<c;
       else g<<c+b; 
	 f.close();
	 g.close();
	 return 0;
}