#include "bits/stdc++.h"
using namespace std;
const int N=200010;
int a,b,c,p[N],h[N],is_p[N],l,ans,vis[20];
int h0(int n) {
    while (n>=10) {
        int m=0;
        while (n) m+=n%10,n/=10;
        n=m;
    }
    return n;
}
int main() {
    memset(is_p,0x3f,sizeof(is_p));
    is_p[0]=is_p[1]=0;
    for (int i=2;i*i<N;++i)
        if (is_p[i])
            for (int j=i*i;j<N;j+=i)
                is_p[j]=0;
    cin>>a>>b;
    for (int i=a;i<=b;++i)
        if (is_p[i]) ++c,p[c]=i,h[c]=h0(i);
    assert(c>=1);
    for (int i=1,j=2;i<=c;++i) {
        vis[h[i]]=1;
        if (i==j) ++j;
        while (j<=c) {
            if (vis[h[j]]) break;
            vis[h[j]]=1;
            ++j;
        }
        if (l<=j-i) l=j-i,ans=p[i];
        // if (j>b) break;
        vis[h[i]]=0;
    }
    cout<<ans<<endl;
    return 0;
}