#include <iostream>
#include <bitset>
using namespace std;

int main()
{
	const size_t MAX = 1000000;

	bitset<MAX> primebox;
	primebox.set();
	primebox.reset(0);
	primebox.reset(1);

	for(int i = 2; i < MAX; i++)
	{
		if(!primebox.test(i))
			continue;

		for(int j = i*2; j < MAX; j += i)
			primebox.reset(j);
	}

	size_t n;
	while(cin >> n)
	{
		int found;
		if(n < 2)
			found = 0;
		else if(n == 2)
			found = 1;
		else
		{
			found = 1;
			for(size_t i = 3; i <= n; i += 2)
				if(primebox.test(i))
					found++;
		}

		cout << found << endl;
	}

	return 0;
}