#include <iostream>
#include <fstream>

using namespace std;

int N;
bool prim[2000001];

int main(int argc, char *argv[]) {
	ifstream fin("ciur.in");
	fin >> N;
	fin.close();

	memset(prim, 1, sizeof(prim));
	int cnt(1);
	for (int i = 3; i <= N; i += 2) {
		if (!prim[i])
			continue;
		++cnt;
		int i2 = 2*i;
		for (int j = i + i2; j <= N; j += i2)
			prim[j] = false;
	}

	ofstream fout("ciur.out");
	fout << cnt << endl;
	fout.close();

	return 0;
}