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

int main() {
	ifstream fin("ciur.in");
	ofstream fout("ciur.out");
	int n;
	fin >> n;
	
	if (n == 1) {fout << 0; return 0;}
	int cnt = 1;
	bitset<2000001> isprime;
	for (int i = 3; i <= n; i += 2)
		isprime[i] = 1;
	for (int i = 3; i <= n; i += 2) {
		if (isprime[i]) {
			++cnt;
			for (int j = 2*i; j <= n; j += i)
				isprime[j] = 0;
		}
	}
	fout << cnt;
	return 0;
}