a,b = list(map(int,input().split()))

if a < 10 and b < 10:

  print((a*b))

else:

  print((-1))
#20:17

a,b = list(map(int,input().split()))

if 0 < a < 10 and 0 < b < 10:

  print((a*b))

else:

  print((-1))
a, b = list(map(int, input().split()))
if a < 10 and b < 10:
    print((a * b))
else:
    print((-1))

# 20:17
a, b = list(map(int, input().split()))
if 0 < a < 10 and 0 < b < 10:
    print((a * b))
else:
    print((-1))

+# 20:17 -if a < 10 and b < 10: +if 0 < a < 10 and 0 < b < 10: