/*
TASK:rprimes
LANG:C++
*/
#include <iostream>
#include <math.h>
using namespace std;
bool f=false,ff=false;
short int aa[100000000];
unsigned long i,j,k,a,b,br=0,x,d,y,c,z,q;
//int y;
void prov()
{
     int ii;
     bool fl=false;
     if (y==1) { f=true; return; }
     if (aa[y]==5) {f=true; return; }
     if (aa[y]==7)  return;
     for (ii=2; ii<=sqrt(y); ii++)
      if (y%ii==0 && ii!=y) { f=true; aa[y]=5; return; }
     aa[y]=7;
}
int main()
{
    cin >> a >> b;
    for (x=a; x<=b; x++)
    {
        if (x>999999999) d=10;
        else
        if (x>99999999) d=9;
        else
        if (x>9999999) d=8;
        else
        if (x>999999) d=7;
        else
        if (x>99999) d=6;
        else
        if (x>9999) d=5;
        else
        if (x>999) d=4;
        else
        if (x>99) d=3;
        else
        if (x>9) d=2;
        else
        d=1;
        y=0;
        z=x;
        c=1;
        for (j=1; j<d; j++)
            c*=10;
        f=false;
        for (j=1; j<=d; j++)
        {
            q=z/c;
            z=z%c;
            c=c/10;
            y=y*10+q;
            prov();
            if (f==true) break;
        }
        if (f==false) br++;
    }
    cout << br;
    return 0;
}
