fun main() {
    val builder = StringBuilder()

    val (a, b) = readInputLine().split(" ").map { it.toLong() }

    if (b == 0L) {
        builder.appendLine(1)
    } else {
        builder.appendLine(
            when(a) {
                -1L -> 2
                else -> -1
            }
        )
    }

    print(builder.toString())
}

fun readInputLine(): String {
    return readLine()!!
}