#include <iostream>
#include <algorithm>
using namespace std;
const int N=200001;
int c[N], memo[N], p[N];
int func(int n)
{
    if (n<10) return n;
    int& res=memo[n];
    if (res) return res;
    int t=0;
    while (n) { t+=n%10; n/=10; }
    return res=func(t);
}
int main()
{
    c[0]=c[1]=1;
    for(int i=2;i*i<N;++i) if (!c[i])
        for(int j=i*i;j<N;j+=i) c[j]=1;


    int n, k;
    while (cin>>k>>n) {
        int m=0, res=0, maxlen=0, s=0, e=0, a[10]={};
        for(int i=k;i<=n;++i) if (!c[i]) {
            p[m++]=i;
            e=m-1;
            if (++a[func(i)]>1) {
                fill(a, a+10, 0);
                for(int j=0;j<10;++j) {
                    if (a[func(p[m-1-j])]) break;
                    ++a[func(p[m-1-j])];
                    s=m-1-j;
                }
            }
            if (maxlen<=e-s+1) {
                maxlen=e-s+1;
                res=p[s];
            }
        }
        cout<<res<<endl;
    }
}