# No.44 DPなすごろく
def main():
    N = int(input())
    # dp[i] := possible move on i-th position
    dp = [0] * (N + 1)
    dp[:2] = 1, 1
    for i in range(2, N + 1):
        dp[i] = dp[i - 2] + dp[i - 1]
    print(dp[-1])


if __name__ == "__main__":
    main()