person = int(input())


def get_commits(person, dict={}):
    # print(f'Starting with {person}')
    if person == 0:
        return 1
    elif person == 1:
        return 1
    elif person > 1:
        # print(f'Get person {person - 1} and {person - 2}')
        if person not in dict:
            first = get_commits(person - 2, dict)
            dict[person - 2] = first
            second = get_commits(person - 1)
            dict[person - 1] = second
            sum = first + second
            dict[person] = sum
        else:
            sum = dict[person]
        return sum

print(get_commits(person))