def fib(n):
    fib_list = list()
    fib_list.append(0)
    fib_list.append(1)
    for i in range(n+1):
        if i >= 2:
            summ = fib_list[i-1]+fib_list[i-2]
            fib_list.append(summ)

    return fib_list[n]


def main():
    n = int(input())
    print(fib(n))


if __name__ == '__main__':
    main()