#include <iostream>
using namespace std;
const int N = 1e7 + 10;

int a, b, cnt;
int primes[N];
bool st[N];

int get_primes(int x)
{
	for (int i = 2; i <= x; i ++ )
	{
		if (!st[i]) primes[cnt ++] = i;
		for (int j = 0; primes[j] <= x / i; j ++ )
		{
			st[primes[j] * i] = true;
			if (i % primes[j] == 0) break;
		}
	}
}

int main()
{
	get_primes(N);
	while (cin >> a >> b)
	{
		int res = 0;
		for (int i = a; i <= b; i ++ ) if (st[i]) res ++;
		cout << res << endl;
	}
	return 0;
}