#include <stdio.h>
int n;
void fibonacci ()
{
     int a=1,b=2,c,i;
     scanf ("%d",&n);
     if (n==1 || n==2)
     {
        printf ("%d",n);return ;
     }
     for (i=3; i<=n; ++i)
     {
         c=a+b;
         a=b;
         b=c;
     }
     printf ("%d",c);
}
int main ()
{
	freopen ("nunta.in","r",stdin);
	freopen ("nunta.out","w",stdout);
	fibonacci ();
	return 0;
}