import java.io.BufferedReader;
import java.io.InputStreamReader;
public class AB {
    public static void main(String[] args) throws Exception
    {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        int a = Integer.parseInt(reader.readLine());
        int b = Integer.parseInt(reader.readLine());
        System.out.println(a+b);

    }
}

У меня такое же решение. Тоже не принимает...

Numbers are located at the same line. So, first call of readLine() give you "a b", and second - null.