#include <stdio.h>
#include <string.h>

long long dp[51];

long long search(int i) {
	if (i == 0) return 1;
	if (i < 0) return 0;
	if (dp[i] != -1) return dp[i];
	return dp[i] = search(i - 1) + search(i - 2);
}

int main() {
	int n;
	scanf("%d", &n);
	
	memset(dp, -1, sizeof(dp));
	printf("%lld\n", search(n));
	return 0;
}