#include <iostream>
using namespace std;

inline bool check(int n)
{
	for (int i = 2; i*i <= n; i++)
	{
		if (n % i == 0) return false;
	}
	return true;
}

int main()
{
	int n[1000000] = {};
	int x;
	bool f;
	
	for (int i = 2; i <= 1000000; i++)
	{
		f = check(i);
		if (f == true) n[i] = n[i - 1] + 1;
		else n[i] = n[i - 1];
	}

	while (cin >> x)
		cout << n[x] << endl;
	return 0;
}
