How to find Prime String (Final) in java by jayanthi ganesh

import java.util.*;

public class PrimeString {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
String str = sc.nextLine();

    char a = str.charAt(0);
    char b = str.charAt(2);
    char c = str.charAt(1);
    char d = str.charAt(3);
    
    int a1=a;
    int b1=b;
    int s1=a1+b1;
    int c1=c;
    int d1=d;
    int s2=c1+d1;
    int diff = s2-s1;
    
    System.out.println(s1);
    System.out.println(s2);
    System.out.println(diff);
    if (diff%3==0)
    System.out.println("Prime String");
    else
    System.out.println("Casual String");

}

}