Case-Insensitive Substring Search

Given two strings, haystack and needle, your task is to find the first occurrence of needle in haystack while ignoring case differences. The search should be case-insensitive, meaning that uppercase and lowercase letters are treated the same. If needle is found, output its starting index (0-indexed). If needle is not found, output -1.

Note: If needle is an empty string, output 0.

The problem can be expressed in mathematical form as follows: \[ ans = \begin{cases} 0 & \text{if } needle = "" \\ \min \{ i : \text{lower}(haystack)[i:i+|needle|] = \text{lower}(needle) \} & \text{if such an } i \text{ exists} \\ -1 & \text{otherwise} \end{cases} \]

inputFormat

The input consists of two lines:

1. The first line is the string haystack.
2. The second line is the string needle.

outputFormat

Output a single integer representing the starting index (0-indexed) of the first occurrence of needle in haystack (ignoring case), or -1 if needle does not appear in haystack. If needle is empty, output 0.

## sample

Hello, World!
world

7

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