from functools import lru_cache


@lru_cache
def calc_patterns(num: int) -> int:
    match num:
        case 0:
            return 1
        case 1:
            return 1
        case _:
            return calc_patterns(num - 1) + calc_patterns(num - 2)


def main():
    N = int(input())
    print(calc_patterns(N))


if __name__ == "__main__":
    main()