Codeforces 146A LuckyTicket program in java

LuckyTicket.java

import java.math.BigInteger;
import java.util.Scanner;

public class LuckyTicket
{
    public static void main(String[] args)
    {
        Scanner z=new Scanner(System.in);
        int n=z.nextInt();
        String b=z.next();
        BigInteger big=new BigInteger(b);
        boolean flag=true;
        if(b.length()==big.toString().length()){
            for(int j=0;j<=9;j++){
                if(j!=4 && j!=7){
                    if(big.toString().contains(String.valueOf(j))){
                        System.out.println("NO");
                        flag=false;break;
                    }
                }
            }
        }else{
            System.out.println("NO");flag=false;
        }
        int temp=0,xtemp=0;
        int a[]=new int[n];
        if(flag){
            for(int i=1;i<=n/2;i++){
                a[i-1]=Integer.parseInt(big.toString().substring(i-1, i));
                temp+=a[i-1];
            }
            for(int i=n/2+1;i<=n;i++){
                a[i-1]=Integer.parseInt(big.toString().substring(i-1, i));
                xtemp+=a[i-1];
            }
            if(temp==xtemp)
                System.out.println("YES");
            else
                System.out.println("NO");
        }
    }
}