题解 | 添加逗号

# 字符串添加逗号
n1 = input().strip()
n = n1[::-1]
number = []
for i in range(len(n)):
    number.append(n[i])
    if (i+1)%3 ==0 and (i+1) != len(n):
        number.append(",")
result = "".join(number[::-1])
print(result)