#include<bits/stdc++.h>
#define N 2000010

using namespace std;

bool viz[2000000];	
int n,rs;

int main() {
	ifstream cin("ciur.in");
	ofstream cout("ciur.out");
	cin>>n;
	
	for (int i=4; i<n; i+=2) viz[i]=1;
	
	for (int i=3; i<sqrt(n); i+=2) {
		if (!viz[i]) {
			for (int j=i*i; j<n; j+=i) viz[j]=1;
		}
	}
	for (int i=2; i<=n; i++)
		if (!viz[i]) rs++;
	cout<<rs;
	
	return 0;
}