import sys
input=lambda: sys.stdin.readline().rstrip()
k=int(input())
n=int(input())
import bisect
def primes(n):
  is_prime=[True]*(n+1)
  is_prime[0]=False
  is_prime[1]=False
  for i in range(2,int(n**0.5)+1):
    if not is_prime[i]:
      continue
    for j in range(i*2,n+1,i):
      is_prime[j]=False
  return [i for i in range(n+1) if is_prime[i]]
P=primes(n)

def f(x):
  if len(str(x))==1:
    return x
  else:
    ret=x%10+f(x//10)
    if ret>=10:
      return ret%10+1
    else:
      return ret

kk=bisect.bisect_left(P,k)
nn=len(P)
C=[kk-1]*10
lr=0
l=kk-1
for i in range(kk,nn):
  p=P[i]
  pp=f(p)
  if i-max(l,C[pp])>=lr:
    ans=P[max(l,C[pp])+1]
    lr=i-max(l,C[pp])
  l=max(l,C[pp])
  C[pp]=i
print(ans)