#include <stdio.h>
int main(void){
	int val = 0;
	scanf("%d",&val);
	long ans[val + 1];
	
	ans[0] = 1;
	ans[1] = 1;
	for(int i = 2;i <= val;i ++){
		ans[i] = ans[i - 1] + ans[i - 2];
	}
	printf("%ld",ans[val]);
}