I was getting WA for a while because I didnt know that the
test:
10
1
2
is "Unrecoverable error."
I think the problem statement tells this in a wrong way: 'besides no leading zeroes can appear as a result of erroneous copying'.
but this can mean this too: the ACCOUNTANT hasnt copied for example 10 as 01.

This means that no number before or after swapping has leading zeroes. So, the number 10 is written correctly, it can't be result of mistake. As well as number 1.