//Dennis
#include <iostream>
using namespace std;
#define FORN(i,a,b) for (int i=a;i<=b;i++)
const int MAX_PRIME=10000000;	//max prime we'll ever need for this problem
const int SQRT_MAX_PRIME=3163;	//Sqrt(MAX_PRIME) - for Eratosthenes Prime Sieve

bool isprime[MAX_PRIME+1];		//data structure to answer question of "is this a prime?"

//Eratosthenes Prime Sieve
void primeSieve(bool isprime[],int max_prime)
{
	for (int i=0;i<=max_prime;i++) isprime[i]=true;		//assume all isprime
	isprime[0]=false;
	isprime[1]=false;
	for (int prime=2;prime<=SQRT_MAX_PRIME;prime++)
		if (isprime[prime])
			for (int comp=prime*prime;comp<max_prime;comp+=prime)
				isprime[comp]=false;
}

//reverses number
int reversed(int n)
{
	int r=0;
	while(n>0)
	{
		r*=10;	
		r+=n%10;
		n/=10;
	}
	return r;
}

int main()
{
	//precompute primes
	primeSieve(isprime,MAX_PRIME);

	int a,b;
	while(cin>>a>>b && a>0)
	{
		int count=0;		
		FORN(i,a,b) if (isprime[i] && isprime[reversed(i)]) count++;
		cout<<count<<endl;
	}

	return 0;
}