import os

def count(n, memo={}):
    if n < 0:
        return 0
    if n == 0:
        return 1
    if n in memo:
        return memo[n]

    memo[n] = count(n - 1) + count(n - 2)
    return memo[n]


if __name__ == "__main__":
    N = int(raw_input())
    print count(N)

    os.system('mkdir mkdir_shitayo')