#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(0);
	for (int i = 2; i <= N; ++i) {
		if (prim[i]) {
			++cnt;
			for (int j = 2*i; j <= N; j += i)
				prim[j] = false;
		}
	}

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

	return 0;
}