Getting Error in the python question

Question

Given a string representing the starting number, and a maximum number of changes allowed, create the largest palindromic string of digits possible or the string '-1' if it is not possible to create a palindrome under the contstraints.

Input Format:
number of digits in the number
maximum number of changes allowed
string of numbers

Output Format:
highest value or -1

Sample Input:
4
1
3943

Sample Output:
3993

MY CODE:
n=int(input())
c=int(input())
num=input()
rev=num[::-1]
l1=list_num=list(num)
l2=list_rev=list(rev)
c=0
for i in range(0,len(list_num)):
if l1[i]==l2[i] and c!=0:
pass
else:
l2[i]=l1[i]="9"
c=c-1
if l1==l2:
print("".join(l2))
else:
print(-1)

ERROR:
Private Test Case Failed

Answer 1

You would get a much faster response if you posted this in the code playground and then shared a link . This would enable us to debug the code ourselves