#include <cstdio> 
using namespace std;

int a[300], b[300], c[300], n, i, r, j;

int main(){
	
	freopen ("nunta.in", "r", stdin);
	freopen ("nunta.out", "w", stdout);
	
	scanf ("%d", &n);
	a[1]=1; a[0]=1; 
	b[1]=2; b[0]=1;
	
	for (i=3; i<=n; i++){
		r=0;
		for (j=1; j<=b[0]; j++){
			c[j]=a[j]+b[j]+r;
			r=c[j]/10;
			c[j]=c[j]%10;
		}
		j--;
		while (r!=0) { j++; c[j]=r%10; r/=10;}
		c[0]=j;
		
		for (j=0; j<=c[0]; j++){
			a[j]=b[j]; b[j]=c[j];
		}
			
	}
	
	if (n==1) printf ("1");	
	else {
		for (j=b[0]; j; j--) printf ("%d", b[j]);
	}
}