Substring Search

Given two strings, your task is to determine the starting index of the second string (substring) in the first string (main string). In other words, find the index i such that

\(s_1[i,i+|s_2|-1]=s_2\)

where \(|s_2|\) is the length of the substring. If s_2 is an empty string, the answer is defined to be 0. If s_2 is not a substring of s_1, output -1.

Please note that the index is 0-based.

inputFormat

The input consists of two lines. The first line contains the main string s_1. The second line contains the substring s_2 to search for.

If the second line is missing or empty, it should be treated as an empty string.

outputFormat

Output a single integer which is the starting index at which s_2 occurs in s_1. Output -1 if s_2 is not a substring of s_1.

hello
ell

1