/*
TASK:rprimes
LANG:c++
*/
#include<iostream.h>
#include<math.h>
//test(x)=prime(x) && test(x%10)
typedef long num;
num const n=5000;
num res=0;
int prime(num a){
	if(a==1) return 0;
        if(a==2) return 1;
	num sq=(num)sqrt(a);
	for(num i=2;i<=sq;i++){
        	if(a%i==0) return 0;
	}
        return 1;
}
int test(num a){
	int pr=prime(a);
        if(pr){
		if(a<10) return 1;
                return test((num)(a/10));
        }
        return 0;
}
int main(){
	num i,a,b,l1,l2,res=0,current,t1;
	cin>>a;
        cin>>b;
	l1=0;
        l2=4;
	num d[n];
	d[0]=2;
	d[1]=3;
	d[2]=5;
	d[3]=7;
	current=d[0];
	while(d[l2-1]<200000000){  //1 nula po-malko
		//generirai bsi4ki
		t1=10*d[l1];
		if(prime(t1+1)){d[l2]=t1+1;
		l2++;}
		if(prime(t1+3)){d[l2]=t1+3;
		l2++;}
		if(prime(t1+7)){d[l2]=t1+7;
		l2++;}
		if(prime(t1+9)){d[l2]=t1+9;
		l2++;}
                l1++;
	}
	for(i=0;i<l2;i++){
             if(a<=d[i] && b>=d[i]) res++;	
	}
	cout<<res;
	return 0;
}