#pragma  warning (disable:4996)
#include<iostream>
#include<cstdio>
#include<queue>
#include<cstring>
#include<string>
#include<cmath>
#include<algorithm>
#define MAX 1000000
using namespace std;
int amount[MAX];
int vis[MAX];
int prime[MAX];
int main(){
	memset(vis, 0, sizeof(vis));
	memset(prime, 0, sizeof(prime));
	prime[0] = prime[1] = 0;
	int n;
	cin >> n;
	for (int i = 2; i<=n; i++){
		if (!vis[i]){
			
			prime[i] = 1;
			for (int j = i+i; j<=n; j += i){
				vis[j] = 1;
				prime[j] = 0;
				
		}
	}
	int sum = 0;
	for (int i = 2; i <= n; i++){
			if (prime[i]){
				sum++;
			}
		}
		cout << sum << endl;
	return 0;
}