Help me rectify the error, please...

Question

Input:

lnstr = int(input())
strn = str(input())
x = int(input())
y = int(input())

if strn[x].isupper():
a = strn[x].lower()
else:
a = strn[x].upper()

if strn[y].isupper():
b = strn[y].lower()
else:
b = strn[y].upper()

print(strn.replace(strn[x],a).replace(strn[y],b))

Output:

6
Dcoder
0
3
DcoDer

Process finished.

Here, only this string out of numerous test cases it doesn't work.
As you see the 'D' in 0 has not been replaced with 'd'.

Answer 1

This is the question rodwynnejones :

Change in Case-

You will be given a single string and two positive integers
denoting indices. You need to change the case of the
characters at those indices.i.e change uppercase to lowercase
and lowercase to uppercase. It is guaranteed that all
characters in the string are alphabets.

Input
The first line contains N, the length of string.
The next line contains a single string.
Two integers, x and y, in next line separated by space.

Sample Input

6
Dcoder
0 3

Output
Print the string after altering the case of characters at those indices.

Sample Output

dcoDer

Constraints-
1 <= string.length <= 40
O <= x, y <= string.length

Answer 2

MIght be that "replace" will replace all "occurrences" .
The string method "replace" can take a third param....count..so try 1.
Please explain exactly what you are trying to do