#include <iostream.h>
#include <fstream.h>
fstream f("nunta.in",ios::in);
fstream g("nunta.out",ios::out);
long a,b,c,n,i;
int main ()
{
	f>>n;
	a=0;b=1;c=1;
  for(i=1;i<=n;i++){
			a=b;
			b=c;
			c=a+b;
		   }
  g<<c;
 return 0;
}