/*
TASK:rprimes
LANG:C
*/
#include<stdio.h>
int ispr(unsigned long i)
{int j,dl=i/2;
for(j=2;j<=dl;j++)
 {if(i%j==0) return 0;
 }
return 1;
}    
int main()
{unsigned long a,b,i,f=0,br=0;
 scanf("%lu %lu",&a,&b);
 
  for(i=a;i<=b;i++)
   {
    f=i;
     while(f>1)
      {if(f<10 && ispr(f)==1) {br++; f=f/10; break; }
       else if(ispr(f)==1) f=f/10; 
       else break;
      }
     
   }
 printf("%lu",br);
 printf("\n");              
 return 0;
}
    
