#include<stdio.h>
int n,i;
long double c,p=1,a;
FILE *in=fopen("nunta.in","rt"),*out=fopen("nunta.out","wt");
int main()
{
	fscanf(in,"%d",&n);
	/*if(n>4)
		a=1;*/
	for(i=1;i<=n;i++)
	{
		c=p+a;
		a=p;
		p=c;
	}
	fprintf(out,"%.0Lf",c);
	return 0;
}