in.nextToken();
        int n = (int) in.nval;
        byte ch1[] = new byte[n];
        byte ch2[] = new byte[n];
        while (n > 0) {
            in.nextToken();
            ch1[n - 1] = (byte) in.nval;
            in.nextToken();
            ch2[n - 1] = (byte) in.nval;
            n--;
        }
        int ost = 0;
        String answer = "";
        for (int i = 0; i < ch1.length; i++) {
            int a = ost + ch1[i] + ch2[i];
            if (a > 9) {
                answer = (a % 10) + answer;
                ost = a / 10;
            } else {
                answer = a + answer;
                ost = 0;
            }
        }
        out.print(answer);

Could someone help with time optimization?