def prime_factors(N):
    res = []
    for i in range(2, int(N ** 0.5) + 1):
        while N % i == 0:
            res.append(i)
            N //= i
    if N != 1:
        res.append(N)
    return res

def divisors(N):
    res = 0
    for i in range(1, int(N ** 0.5) + 1):
        if N % i == 0:
            res += 1
            if i * i != N:
                res += 1
    return res

N, K = map(int, input().split())
N_pf = prime_factors(N)
#print(N, N_pf)
ma, ans = 0, -1
for M in range(N):
    i_pf = prime_factors(M)
    j = 0
    cnt = 0
    #print(M, i_pf)
    for p in i_pf:
        if j < len(N_pf) and p in N_pf[j:]:
            j = j + N_pf[j:].index(p) + 1
            cnt += 1
    if cnt >= K:
        d = divisors(M)
        if ma < d:
            ma = d
            ans = M
print(ans)