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