i have understood the formula for it but i am unable to understand that when k=-1 and n and m have different parity the answer will be -1 but for k=1 answer will not be -1 why?problem
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i have understood the formula for it but i am unable to understand that when k=-1 and n and m have different parity the answer will be -1 but for k=1 answer will not be -1 why?problem