/*
TASK:rprimes
LANG:C++
*/
#include<iostream>
#include<vector>
#include<cmath>
using namespace std;
vector<long long int> p;
vector<long long int> q;
long long int a,b;
int prime(long long int y)
{
if(y==1)return 0;
    long long int i,f=sqrt(y);
    for(i=2;i<=f;i++)
    {
                     if(y%i==0)return 0;
    }
return 1;
}
int dig(long long int h)
{
    int br=0;
    while(h)
    {
            br++;
            h/=10;
    }
    return br;
}
int main()
{
    cin>>a>>b;
    int x=dig(b);
    
    
p.push_back(2);
p.push_back(3);
p.push_back(5);
p.push_back(7);
long i,j,k;

long long int o,BR=0;
if(a<=2)BR++;
if(a<=3)BR++;
if(a<=5)BR++;
if(a<=7)BR++;
for(i=1;i<x;i++)
{
for(j=0;j<p.size();j++)
{o=p[j]*10;
                       for(k=1;k<10;k+=2)
                       {
                                         if(prime(o+k)){q.push_back(o+k);if((o+k)<=b&&(o+k)>=a){BR++;}if((o+k)>=b){cout<<BR<<endl;exit(0);}}
                       }

}
p=q;
q.clear();
}

    cout<<BR<<endl;
return 0;
}
