def GCD (a,b)
    if (a==0 && b==0)
        return -1
    end
    if (a==0 || b==0)
        return a+b
    end
    return GCD(b,a%b)
end
def LCM (a,b)
    if (a==0 || b == 0)
        return -1
    end
    return (a*b).abs/GCD(a,b)
end
def Ck(a,b)
    r = 1
    a.times do |i|
        r = r*b/(i+1)
        b-=1
    end
    return r
end
def isOdd a
    if (a&1)


a = 8
b = 10
puts GCD(a,b)
puts LCM(a,b)
puts Ck(a,b)