#include <bits/stdc++.h>
using namespace std;

int n,k;
bool sir[2000000];

int main() {
	ifstream cin("ciur.in");
	ofstream cout("ciur.out");
	cin >> n;
	memset(sir, true, sizeof(sir)); 
	for (int p=2;p*p<=n;p++) {
		if (sir[p]==true) {
			for (int i=p*p; i<=n; i+=p) {
				sir[i]=false;
			}
		}
	}
	for (int i=2; i<=n; i++) {
		if (sir[i]==true)k++;
	}
	cout << k;
}