#include<iostream>
#include<cstdio>
#include<cmath>
#define _for(i,a,b) for (int i=(a);i<=(b);i++)//更方便
using namespace std;
int reverse(int x){//返回其回文串
    int ans=0;//注意初始化
    while (x){
        ans=ans*10+x%10;
        x/=10;
    }
    return ans;
}
bool is_prime(int a){//判断是否属质数
    int m=sqrt(a);
    for (int i=2;i<=m;i++){
        if (a%i==0){
            return false;
        }
    }
    return true;
}
int main(){
    freopen("count.in","r",stdin);
    freopen("count.out","w",stdout);
    int l,r,ans=0;
    scanf("%d%d",&l,&r);
    _for(i,l,r){
        if (reverse(i)==i && is_prime(i)){//判断
            ans++;
        }
    }
    printf("%d\n",ans);
    return 0;
}