#include <iostream>
using namespace std;

long long a,b,sol;

int snaga(int x)
{
    int num = 1;
    while (x != 2)
        {
            for (int i=2; i<x; i++)
                if (x % i != 0)
                    {
                        x = i; num++; break;
                    }
        }

    return num;
}

int main (void)
{
    cin >> a >> b;

    for (int i=a; i<=b; i++)
        sol += snaga(i);

    cout << sol << endl;

    return 0;
}