题解 | #添加逗号#

n=input()
n=n[::-1]
number=[]
cnt=1
for i in range(len(n)):
    if cnt%3==0:
        number.append(n[i])
        if cnt<len(n):
            number.append(',')
        cnt+=1
    else:
        number.append(n[i])
        cnt+=1
number=number[::-1]
for x in number:
    print(x,end='')