/*
TASK:rprimes
LANG:C++
*/
#include<iostream>
using namespace std;
long long a[85]={2,3,5,7,23,29,31,37,53,59,71,73,79,233,239,293,311,313,317,373,379,593,599,719,733,739,797,2333,2339,2393,2399,2939,3119,3137,3733,3739,3793,3797,5939,7193,7331,7333,7393,23333,23339,23399,23993,29399,31193,31379,37337,37339,37397,59393,59399,71933,73331,73939,233993,239933,293999,373379,373393,593933,593993,719333,739391,739393,739397,739399,2339933,2399333,2939999,3733799,5939333,7393913,7393931,7393933,23399339,29399999,37337999,59393339,73939133};
int main()
{
    long long x,y,i,br=0,j;
    cin>>x>>y;
//    cout<<a[2];
    for(i=0;a[i]<x;i++);

    for(j=i;a[j]<y&&j<83;j++)br++;
//        cout<<a[j]<<endl;
    cout<<br<<endl;
    return 0;
}
    
    
