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

    print(dp[n])


if __name__ == '__main__':
    main()