a, b, c = '='.join(input().split('+')).split('=')
for i in range(2, 37):
    try:
        a1, b1, c1 = int(a, i), int(b, i), int(c, i)
    except ValueError:
        continue
    else:
        if a1 + b1 == c1:
            print(i)
            break
else:
    print(-1)