Find the First Occurrence of a Substring

Given two strings, a main string and a substring, your task is to find the index of the first occurrence of the substring in the main string. The search is case-sensitive and only exact matches are considered.

If the substring does not appear in the main string, output -1.

You need to find the smallest index i (0-indexed) such that:

$$ main\_string[i:i+|sub\_string|] = sub\_string $$

If no such index exists, output \(-1\).

Examples:

• For main string "hello" and substring "ll", the answer is 2.
• For main string "hello" and substring "LL", the answer is -1.
• For main string "abcdabcd" and substring "bc", the answer is 1.

inputFormat

The input is provided via stdin and consists of two lines:

1. The first line contains the main string.
2. The second line contains the substring to search for.

outputFormat

The output should be printed to stdout and is a single integer: the index (0-indexed) of the first occurrence of the substring in the main string. If the substring is not found, output -1.

## sample

hello
ll

2