import sys
input = sys.stdin.readline
from bisect import bisect_left
INF = 1 << 30

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