#include <bits/stdc++.h>
using namespace std;
bool isPrime(int n)
{
	if (n < 2)
	{
		return 0;
	}
	for (int i = 2; i * i <= n; i++)
	{
		if (n % i == 0)
		{
			return 0;
		}
	}
	return 1;
}
int main()
{
	int a, b;
	cin >> a >> b;
	int cnt = 0;
	for (int i = a; i <= b; i++)
	{
		if (isPrime(i) == 1)
		{
			int t = i;
			int newi = 0;
			while (t != 0)
			{
				int t1 = t % 10;
				newi = newi * 10 + t1;
				t = t / 10;
			}
			if (newi>=a and newi<=b)
			{
			if(isPrime(newi) == 1){
			cnt++;
			}
			}
		}
	}
	cout<<cnt;
	return 0;