A, B = (int(i) for i in input().split())  
if 1 <= A < 10 and  1 <= B < 10 :
    ans = A * B
    print({}.ans)
else :
    print(str(-1))A, B = (int(i) for i in input().split())  
if 1 <= A < 10 and  1 <= B < 10 :
    ans = A * B
    print(ans)
else :
    print(str(-1))