19分，有一个测试点为非零返回
import math


l,k = map(int,input().split(" "))

n = input()

for i in range(l-k+1):
    flag = 1
    num = int(n[i:i+k])
    if num%2 == 0 and num != 2:
        flag = 0
    elif num in [1,2,3,5,7]:
        pass
    else:
        for j in range(3,int(math.sqrt(num))+1,2):
            if num%j == 0:
                a = num
                flag = 0
                break
    if flag:
        print(str(num).zfill(k))
        break
if flag == 0:
    print("404")