import streams, sequtils, strutils, algorithm, math, future, sets, tables, hashes
proc `ceilDiv`*[T](x, y: T): T = x div y + ord(x mod y != 0)
proc `//=`*(x: var SomeInteger; y: SomeInteger) = x = x div y
proc `%=`*(x: var SomeInteger; y: SomeInteger) = x = x mod y

var
    L = stdin.readLine.split.map(parseInt)
    A = L[0]
    B = L[1]
    N = 0
    Np = 0
Np = B
N = A * Np + B
if Np == 0:
    echo 1
elif N == 0:
    echo 2
else:
    echo -1