#最大公約数
def gcd(a,b):
    while b!=0:
        a,b=b,a%b
    return a

 #最小公倍数
def lcm(a,b):
    return a*b//gcd(a,b)

A,B=map(int,input().split())

if A==1 or B==1:
    print(0)
    exit()

Al=[]
for i in range(1,int(A**0.5)+1):
    if A/i==A//i:
        Al.append(i)
        Al.append(A//i)
#print(Al)

for item in Al[1:]:
    if B%item==0:
        print(-1)
        exit()

eu=(lcm(A,B))

ans=0
for num in range(1,eu):
    org=num
    while num>-1:
        if num%B==0:
            ans+=1
            break
        else:
            num-=A
print(eu-ans-1)