Python 计算1-1/2+2/3-3/5*4/8-5/13

Question

计算1-1/2+2/3-3/5*4/8-5/13前n项和，n由用户输入

Answer 1

sum = 1
n=int(input())
flag = -1
a=1
b=2
c=0
for i in range(1,n):
    sum += i/b*flag
    flag = -flag
    c=a
    a=b
    b=b+c
print(sum)