1 def number(num):
2 a=0
3 b=1
4 i=2
5 s=1
6 if num==2:
7 return 1
8 else:
9 while 1:
10 if i<num:
11 a, b = b, a+b
12 s = s+b
13 i = i+1
14 else:
15 break
16 return s
17
18 if __name__ == '__main__':
19 num = input("请输入N")
20 if num.isdigit() and int(num)>=2:
21 res = number(int(num))
22 print(res)
23 else:
24 print("输入有误")