while True:
    try:
        month = int(input())
        count, n1, n2 = 2, 1, 1
        if month < 3:
            print(1)
        else:
            while count < month:
                nth = n1 + n2
                n1 = n2
                n2 = nth
                count += 1
            print(n2)
    except:
        break