UVA - 10433 - Automorphic Numbers

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.math.BigInteger;

public class Main{

    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        StringBuilder sb = new StringBuilder();  
        String m="";
        while((m=br.readLine())!=null){
            int val=checkBg(m);
            if(val==0){
                sb.append("Not an Automorphic number.\n");
            }else{
                sb.append(String.format("Automorphic number of %d-digit.\n", val));
            }
        }
        System.out.print(sb);
    }
   
    static int checkBg(String m){
       
        BigInteger bg=new BigInteger(m);
        int n=m.length();
        String str=bg.modPow(BigInteger.valueOf(2), BigInteger.TEN.pow(n)).toString();
        if(str.equals("0") ||str.equals("1"))
            return 0;
        while(str.length()!=n){
           str="0"+str;
        }
        for(int i=0;i<n;i++){
            if(str.charAt(i)!=m.charAt(i))
                return 0;
        }
        return n;
    }
}