k=int(input())
n=int(input())
p=[1]*-~n
p[0]=p[1]=0
h=[None]*-~n
h[:10]=*range(10),
for i in range(n+1):
    if p[i]:
        for j in range(i*i,n+1,i):p[j]=0
    h[i]=h[sum(map(int,str(i)))]
h=[(h[i],i)for i in range(k,n+1)if p[i]]+[[0,0]]
s={0}
m=len(h)-1
p=0
r=(0,0)
for i in range(m):
    while h[p][0] not in s:s|={h[p][0]};p+=1
    r=max(r,(p-i,h[i][1]))
    s^={h[i][0]}
print(r[1])