n,k=map(int,input().split())
ans=1
mod=10**k
n%=mod
m=0
a=n
for i in range(1,k+1):
    flag=True
    m=n
    q=1
    for j in range(1,11):
        m*=a
        m%=mod
        q*=a
        q%=mod
        if m%10**i==n%10**i:
            ans*=j
            a=q
            flag=False
            break
    if flag:
        print(-1)
        exit(0)
print(ans)