K-th Character in String Game II

A game starting with the string "a". In each round, append each character incremented by a value that doubles each round (1, 2, 4, 8, ...). Find the k-th character (1-indexed) after enough rounds. The character is determined by 'a' + ((k - 1) % 26).

Examples
Input: 1
Output: "a"
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K-th Character in String Game II

A game starting with the string `"a"`. In each round, append each character incremented by a value that doubles each round (1, 2, 4, 8, ...). Find the k-th character (1-indexed) after enough rounds. The character is determined by `'a' + ((k - 1) % 26)`.