def fib(n):
    if n < 1:
         return None
    if n < 3:
        return 1

    elem1 = elem2 = 1
    s = 0
    for i in range(3, n + 1):
        s = elem1 + elem2
        elem1, elem2 = elem2, s
    return s

#print(fib(4))
for n in range(1, 21):
	print(n, "->", fib(n))