# import sys; input = sys.stdin.buffer.readline
# sys.setrecursionlimit(10**7)
from collections import defaultdict
con = 10 ** 9 + 7; INF = float("inf")

def getlist():
	return list(map(int, input().split()))

#処理内容
def main():
	N = int(input())
	DP = [0] * 52
	DP[0] = 1
	for i in range(50):
		DP[i + 1] += DP[i]
		DP[i + 2] += DP[i]

	print(DP[N]) 


if __name__ == '__main__':
	main()