Hello ladies and gentelmen! Could you please explain me what is wrong with my code and why it fails the test #2. I have read in a previous post that

Result for test
4
9 0
5 4
5 4
5 5
must be "0000"

and my code passes it.
Thank you in advance. Here is my code:

import java.util.*;
import java.text.DecimalFormat;

public class JavaApplication8 {

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

        int n = sc.nextInt();
        int a, b, r = 0, plus = 0;
        String pattern = "";

        for(int i=0;i<n;i++)
        {
            a=sc.nextInt();
            b=sc.nextInt();
            plus = a+b;
            r += (plus%10) * Math.pow(10, n-i-1);
            if(plus>9)r += Math.pow(10, n-i);
            pattern+="0";
        }

        r%=Math.pow(10,n);
        sc.close();

        DecimalFormat myFormatter = new DecimalFormat(pattern);
        String output = myFormatter.format(r);
        System.out.println(output);
    }

}