#include<stdio.h>
int n;
int fib(int n)
{
	int i,x,y,z;
	x=y=1;
	z=x+y;
	for(i=3;i<=n;i++)
	{
		x=y;
		y=z;
		z=x+y;
	}
	return z;
}
int main()
{
	freopen("nunta.in","r",stdin);
	freopen("nunta.out","w",stdout);
	scanf("%d",&n);
	if(n==1)
	{
		printf("1\n");
		return 0;
	}
	if(n==2)
	{
		printf("2\n");
		return 0;
	}
	printf("%d\n",fib(n));
	return 0;
}