https://www.e-olymp.com/az/problems/22

/*
    Author: Kanan Asgarli
    https://www.e-olymp.com/az/problems/22
*/
#include <iostream>
#include <cmath>
#define const 10000

using namespace std;
int a, b, p[const+1], res, c;
void primes(){
    p[1] = 1;
    for(int i = 2; i <= (int)sqrt(const); i++)
        if(p[i] == 0)
            for(int j = i*i; j <= const; j += i)
                p[j] = 1;
}
int reverse(int n){
    int l = 0, d[5], m = 0, rev = 0;
    while(n > 0){
        d[l++] = n%10;
        n = n/10;
    }
    for(int i = 0; i < l; i++){
        rev = rev*10 +d[i];
    }
    return rev;
}
int main()
{
    primes();
    cin>>a>>b;
    if(a > b)
        swap(a,b);
    for(int i = a; i <= b; i++){
        if(p[i] == 0 && p[reverse(i)] == 0)
            res++;
    }
    cout<<res<<endl;

    return 0;
}