#include<cstdio>
#include<vector>


using namespace std;


int is_prime(int x)
{
	int i;

	if(x<2) return 0;
	if(x%2==0) return (x==2);

	for(i=3;i*i<=x;i+=2)
	{
		if(x%i==0) return 0;
	}
	return 1;
}


int fhash(int x)
{
	int r;

	for(;x>9;)
	{
		r=0;
		for(;x;)
		{
			r+=x%10;
			x/=10;
		}
		x=r;
	}
	return x;
}


int solve(int k, int n)
{
	vector<int> p, h;
	int i, s, e, l, l_max=0, s_max=0;
	int c[10]={0};

	for(i=k;i<=n;i++)
	{
		if(is_prime(i))
		{
			p.push_back(i);
			h.push_back(fhash(i));
		}
	}

	for(s=e=0;e<h.size();e++)
	{
		c[h[e]]++;
		for(;c[h[e]]>1;s++)
		{
			c[h[s]]--;
		}
		l=e-s+1;
		if(l_max<=l)
		{
//			printf("update l=%d p[s]=%d p[e]=%d\n", l, p[s], p[e]);
			l_max=l;
			s_max=s;
		}
	}
	return p[s_max];
}


int main(void)
{
	int k, n;

	while(scanf("%d%d", &k, &n)==2)
	{
		printf("%d\n", solve(k, n));
	}

	return 0;
}