#include<stdio.h>
#include<math.h>

int f[45];

int main()
{
	int n;
	f[0] = 1, f[1] = 1;
	for (int i = 2; i < 45; i++)
		f[i] = f[i - 1] + f[i - 2];
	scanf("%d", &n);
	printf("%d\n", f[n]);
	return 0;
}