n = int(input('请输入要一个整数：'))
n_2 = 0
n_1 = 1
current = 1
for x in range(2, n+1):
  current = n_2 + n_1
  n_2 = n_1
  n_1 = current
print('第%d个数是%d'%(n, current))

def fab(n):
  if n == 1 or n == 2:
    return 1
  return fab(n-1) + fab(n-2)

print(fab(5))

def fib(n):
  a, b = 0, 1
  for _ in range(n):
    a, b = b, a + b
    yield a
    
for val in fib(20):
  print(val)