#include <stdio.h>

int main() {
	int n, i;
	scanf("%d", &n);
	
	long long dp[51] = { 1,1 };
	for (i = 2; i <= n; i++)
		dp[i] = dp[i - 2] + dp[i - 1];

	printf("%lld\n", dp[n]);
	return 0;
}