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5KfbGQiriNxxwMKgdpwmu5ZsYyXBuBaCg7es9z5xznAnCEHzy51: True
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Looking at the code: it uses an invalid wif(5KgbGQiriNxxwMKgdpwmu5ZsYyXBuBaCg7es9z5xznAnCEHzy51) and then replaces a character with every possible value. So every time this leads to a different wif to check. The result you see counting from 1..50 is the position where it tries the different possible values. A success was found by replacing the third character from a "g" to "f" leading to a valid wif.
Incorrect wif at start:
5KgbGQiriNxxwMKgdpwmu5ZsYyXBuBaCg7es9z5xznAnCEHzy51
Corrected to:
5KfbGQiriNxxwMKgdpwmu5ZsYyXBuBaCg7es9z5xznAnCEHzy51
All the other substitutions didn't lead to a valid wif, that's why you see the counter go up to 50 without any other success messages.
Disclaimer: I'm not the author of the code just explaining the code