1ая задача втрой лабы

with open('input.txt', 'r') as InputFile:
    R = InputFile.read()
    R= int(R)
First =  (R//1000)%10
Second = (R//100)%10
Third =(R//10)%10
Fourth = R%10
i=0
while (i<5):
    if(First>Second and Second>0):
        a=First
        First=Second
        Second= a
    elif (Second>=Third ):
        a=Second
        Second= Third
        Third= a
    elif(Third>=Fourth):
        a= Third
        Third = Fourth
        Fourth = a
    i+=1
First= str(First);Second= str(Second);Third= str(Third);Fourth= str(Fourth);
with open('output.txt', 'w') as OutputFile:
    OutputFile.write(First+Second+Third+Fourth)