import java.util.*;
import java.lang.*;
import java.io.*;

class Main {
	public static void main (String[] args) throws java.lang.Exception
	{
		int a, b;
    	int number1, number2;
	   	int counter = 0;
		Scanner sc = new Scanner(System.in);
		a = sc.nextInt();
		b = sc.nextInt();
		if(a > b) {
			a += b;
			b = a - b;
			a -= b;
		}
		if (a == 1) counter--;
		for (int i = a; i <= b; i++){
			number1 = i; 
			boolean f1 = true;
			boolean f2 = true;
			for (int j = 2; j*j <= number1; j++){					
				f1 = ((number1%j)!=0);
				if (!f1) 
				break;
			}
         	if (f1){
				number2 = 0;
				while (number1 > 0) {
					number2 = number2*10 + number1%10;
					number1 /= 10;
				}
				for (int j = 2; j*j <= number2; j++){
					f2 = ((number2%j)!=0);
					if (!f2) break; 
				}
             	if (f2) counter++; 
         	}
		}
		System.out.format("%d", counter);
	}
}