#include <bits/stdc++.h>

using namespace std;
bool is_prime (int x)
{
    for (int i = 2; i*i<=x; ++i)
        if (x%i==0)
        return 0;
    return 1;
}
int main()
{
    int v[30], a, b, contor = 0;
    cin >> a >> b;
    v[0] = 2;
    v[1] = 3;
    v[2] = 5;
    v[3] = 7;
    v[4] = 23;
    v[5] = 37;
    v[6] = 53;
    v[7] = 73;
    for (int i = 0; i<=6; ++i)
        if (v[i]>=a && v[i]<=b)
            ++contor;
    cout << contor;
    return 0;
}