/*
TASK:rprimes
LANG:C++
*/
#include <math.h>
#include <iostream>
using namespace std;
long long a,b,br=0;
int isprime(long long x)
     {
      long long i;
      if(x==1)return 0;
      for(i=2;i<=sqrt(x);i++)if(x%i==0)return 0;
      return 1;
      }
int main ()
{
long long i,j,x;
//int j;
bool p;
scanf("%lld%lld",&a,&b);
for(i=a;i<=b;i++)
                 {
                  x=i;
                  p=0;
                  for(;x>0;)
                             {
                             if( isprime(x) == 0)
                                 {p=1;break;}
                                 x/=10;
                              }
                  if(p==1)continue;
                  br++;//printf("%d\n",i);
                  }
printf("%lld\n",br);
}
