from math import *

A, B = map(int, input().split())
if gcd(A, B) != 1:
    print(-1)
    exit()

ans = 0
now = 0
S = set()
while True:
    if now % B in S:
        print(ans)
        exit()
    S.add(now % B)
    ans += now // B
    now += A