#include<stdio.h>

int n,c,a,b,i;

int main(){
	FILE*f=fopen("nunta.in","r");
	FILE*g=fopen("nunta.out","w");
	fscanf(f,"%d",&n);
	a=1;
	b=2;
	if(n==1)
		fprintf(g,"1");
	else{
		if(n==2)
			fprintf(g,"2");
		else{
			i=3;
			while(i<=n){
			c=a+b;
			a=b;
			b=c;
			i++;
			}
			fprintf(g,"%d",c);
		}	
	}
	fclose(f);
	fclose(g);
	return 0;
}