/*
TASK:rprimes
LANG:C++
*/
#include<iostream>
#include<math.h>
 using namespace std;
 int main()
 {
 unsigned long int a,b,c=0,d;
 bool ch=1;
 cin>>a>>b;
 if(a%2==0)
 	 a=a+1;
 for(int i=a;i<=b;i+=2)
 {
     d=i; 		 
	 while(d)
	 {
		 if(((d%2==0)&&(d!=2))||(d==1))
         {
		     ch=0;
		     break;
         }
    	 for(int j=3;j<=sqrt(d);j+=2)
    	     if(d%j==0)	 
		     {
	  			 ch=0;
		         break;
		     }
	    		 d/=10;
	   
		 	 	   		
     }
       if(ch)
	     c++;
	     ch=1;
 }
 if(a<3)
 	 c++;
 cout<<c;
 system("pause");
 return 0;
}
 


