/*
TASK:rprimes
LANG:C++
*/
#include <iostream>
using namespace std;
int p[16480000];

int rprime(int a){
    int b=1;
    while((a+9)/10!=0){if (p[a]==1){b=0;break;}
    a/=10;}
    return b;
}

int main(){
    int a,b;
    cin >> a >> b;
    p[1]=1;
    for(int i=2;i<b/2;i++) if (p[i]==0){
    for(int j=i;j<=b;j+=i) p[j]=1;p[i]=0;}
    int br=0;
    for(int i=a;i<=b;i++) if (rprime(i)==1) br++;
    cout << br << endl;
    return 0;
}
