def main():
    n = int(input())
    dp = [0 for i in range(n + 1)]
    dp[0] = 1
    for i in range(len(dp)):
        if dp[i]:
            if i + 1 < len(dp):
                dp[i + 1] += dp[i]
            if i + 2 < len(dp):
                dp[i + 2] += dp[i]

    print(dp[n])

if __name__ == '__main__':
    main()