
import java.io.BufferedInputStream;
import java.math.BigInteger;
import java.util.*;

public class abc {
    public static void main(String[] args) {
        Scanner in = new Scanner(new BufferedInputStream(System.in));
        int a = in.nextInt();
        int b = in.nextInt();
        for (int i = 0; ; i++) {
            if (1 <= a && a <= 9 && b >= 1 && b <= 9) {
                System.out.println(a + b);
                a = in.nextInt();
                b = in.nextInt();
            }
            else{
                System.out.println(-1);
                break;
            }
        }
    }
}



