#include<stdio.h>

int main(void){
	int N,i;
	long long memo[51];

	scanf("%d",&N);

	memo[0] = 1;
	memo[1] = 1;
	for(i=2;i<=N;i++){
		memo[i] = memo[i-1] + memo[i-2];
	}
	printf("%lld\n",memo[N]);
}