MOD = 10 ** 9 + 7
INF = 10 ** 15

def main():  
    X,Y = map(int,input().split())
    if X == Y:
        print(0)
    elif Y == 0:
        print(1)
    elif X == 0:
        print(2)
    else:
        print(-1)
if __name__ == '__main__':
    main()