/*
TASK:rprimes
LANG:C++
*/
#include<iostream>
using namespace std;
unsigned long long int a,b,br=0,c;
int main()
{
    int t=0;
    cin>>a>>b;
    for(unsigned long long int i=a;i<=b;i++)
    {
                 c=i;
                 for(unsigned long long int j=0;j<10;j++)
                 {
                              if(c>=10&&c<=19){t=1; break;}
                              if(t>0||c==0||c==1) break;
                 for(unsigned long long int g=2;g<b/2+1;g++)
                 {
                              if(c%g==0&&c!=g)
                              {
                                              t=1;
                                              break;
                              }
                 }
                 c=c/10;}
                 if(t!=1)
                 {br++; }t=0;
    }
    cout<<br;
    system("pause");
    return 0;
}
