#!/usr/bin/env python3


def solve(a, b):
    if a == 1 and b == 0:
        return 1
    elif a == -1:
        return 2
    else:
        return -1


def main():
    a, b = (int(z) for z in input().split())
    res = solve(a, b)
    print(res)


if __name__ == "__main__":
    main()