#include <fstream>

using namespace std;

#define LIMIT (1<<15)
bool ciur[2000005];

int main()
{
	ifstream fin("ciur.in");
	ofstream fout("ciur.out");

	int N;
	fin >> N;

	int cnt = 0;
	for (int i = 2; i <= N; ++i) {
		if (ciur[i] == 0) {
			++cnt;
			if (i > LIMIT) continue;

			for (int j = i * i; j <= N; j += i)
				ciur[j] = 1;
		}
	}

	fout << cnt << '\n';
	return 0;
}