Problem statement

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You are given a string $\text{'}$S$\text{'}$ of length $\text{'}$N$\text{'}$ and an integer $\text{'}$K$\text{'}.\text{'}$K$\text{'}$ is a divisor of $\text{'}$N$\text{'}.$

Suppose you break the string into $\text{'}$M$\text{'}$ subarrays $($where $\text{'}$M$\text{'}=\text{'}$N$\text{'}/\text{'}$K$\text{'}),$ i$.$e$.,$

$$ The first substring $\text{'}$S$1\text{'}$ is $\text{'}$S$[1...$ KJ$\text{'}.$

The second substring $\text{'}$S$2\text{'}$ is $\text{'}$S$[$K $+1...2*$KJ$\text{'}.$

$$ The $\text{'}$M$\text{'}$th substring is $\text{'}$SM$\text{'}$ is $\text{'}$S$[($M$-1)*$ K $+1...$ M$*$ KJ$\text{'}.$

You are allowed to do the following operation:

$$ Choose any index $\text{'}$i$\text{'}$ of the string $\text{'}$S$\text{'}.$

$$ Replace it with any lowercase$$character$.$