#include <stdio.h>
int main ()
{ FILE *f=fopen("nunta.in","r");
FILE *g=fopen("nunta.out","w");
int n,a,b,c,k=0;;
fscanf (f,"%d",&n);
if (n==1) fprintf (g,"1");
else if (n==2) fprintf (g,"2");
	 else { a=1;
			b=2;
	        k=2;
			while (k<n)
				{ c=a+b;
			      a=b;
				  b=c;
				  k++;
				}
			fprintf (g,"%d",c);
		  }
fclose (f);
fclose (g);
return 0;
}