#include<iostream>
#include<vector>
#include<algorithm>
#include<stdio.h>

using namespace std;

long long int A = 0, B = 0, k=0;

int main()
{
	int a[] = { 1, 2, 3, 5, 7, 11, 13, 17, 23, 31, 37, 53, 71, 73, 113, 131, 137, 173, 311, 317, 719 };

	cin >> A >> B;

	k = 0;
	for (int i = 0; i < 21; i++)
	{
		if (a[i] >= A && a[i] <= B)
		{
			k++;
		}
	}
	cout << k;
	return 0;
}