#include <bits/stdc++.h>
using namespace std;

const int maxn = 10000001;
int judge[maxn] = { 0 }; //judge==0 is sushu
int main()
{
	int a, b;
	for (int i = 2; i*i < maxn; i++)
	{
		if (!judge[i])
			for (int j = i * i; j < maxn; j += i)
				judge[j]++;
	}
	while (cin >> a >> b)
	{
		int count = 0;
		for (int i = a; i <= b; i++)
			if (judge[i])
				count++;
		cout << count << endl;
	}
	return 0;
}