Фибоначчи 1№2

n = int(input("Введите число до 40: "))
a = 0
b = 1
if n == 1:
    print(0)
elif n == 2:
    print(1)
elif n < 40 and not n == 1 and not n == 2:
        n = n-2
        for ch in range(n):
            c = a+b
            a = b
            b = c
        print(c)