#include <cstdio>

using namespace std;

int main()
{
    int a, b;
    scanf("%d %d", &a, &b);

    int counter = 0;
    int z;
    int nedi;
    for(int i = a; i < b + 1; i++)
    {
        z = i;
        nedi = z;
        counter++;
        while(nedi > 2)
        {
            for(int p = 2; p < nedi; p++)
            {
                if(nedi % p != 0)
                {
                    nedi = p;
                }
            }
            counter++;
        }
    }

    printf("%d", counter);

    return 0;
}