OTP Generator using Java

This Java code is for generating an OTP (One-Time Password) for a user. The program takes input from the user, which is their phone number, and uses it to generate an OTP using a specific algorithm. The algorithm takes the number, finds the length of the number, then iterates through the number by taking every second character, squares it, and appends the result to a string variable called "otp". Then it takes the first 4 characters of the "otp" variable, converts it to an integer, and assigns it to the variable "m". The program then prompts the user to enter the OTP they received, and compares it with the generated OTP using the check function. If the entered OTP matches the generated OTP, the program prints "Correct", otherwise it calls the "incorrect" function which gives the user the option to either re-enter the OTP or to resend the OTP, and check the entered OTP again.