排序不通过啊

a=int(raw_input("plaese input:\n"))
b=int(raw_input("plaese input:\n"))
c=int(raw_input("plaese input:\n"))
dd=[]
dd.append(a)
dd.append(b)
dd.append(c)
print(type(a))
print(type(b))
print(type(c))
print (dd)
i=0
while (i<=3):
    if dd[i]>i[i+1]:
            dd[i]=dd[i]
    i=i+1
print (dd)


运行后总是提示type error 'int' object is not subscrptable

犯了低级错误...