#include <bits/stdc++.h>

 using namespace std;

 const int M = +;

 double p, q;

 bool prime[M];

 int ans, pri, pal;

 void getprime( )    {   // 类似筛选法求素数 打表

     prime[] = false;

     for( int i=; i<M; i++ )    {

         if( !prime[i] )  continue;

         prime[i] = true;

         for( int j=; j*i<M; j++ )

             prime[i*j] = false;

     }

 }

 bool palindromic( int n )   {   // 判断回文数

     int fn = ;

     int aun = n;

     while( aun )    {

         fn *= ;

         fn += aun%;

         aun /= ;

     }

     return fn == n ;

 }

 int main()  {

     memset( prime, true, sizeof(prime) );

     getprime( );

     while( ~scanf("%lf%lf", &p, &q ) )  {

         double A = p/q;

         pri = pal = ;

         for( int i=; i<M; i++ )    {

             pri += prime[i];

             pal += palindromic(i);

             if( pal*p/q >= pri )

                 ans = i;

         }

         printf("%d\n", ans );

     }

     return ;

 }