#include <cstdio>
#include <vector>

using namespace std;

int main()
{
    //freopen("file.in", "r", stdin);
    //freopen("file.out", "w", stdout);
    vector<int> v={2,3,5,7,11,13,17,23,31,37,53,71,73,113,117,137,317};
    int a,b,nr=0;
    scanf("%d%d",&a,&b);
    for(int i=0;i<v.size();i++)
        if(a<=v[i] && v[i]<=b) nr++;
    printf("%d",nr);
    return 0;
}