#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;
     
    for (int i = 2; i*i <=MAX; i++){
        if (!vis[i]){
            prime[i] = 1;
            for (int j = i+i; j <=MAX; j += i){
                vis[j] = 1;
                prime[j] = 0;
            }
        }
    }
    /*int sum = 0;
    for (int i = 2; i <= MAX; i++){
        if (prime[i]){
            sum++;
        }
        amount[i] = sum;
    }*/
    int n;
     
    while (cin >> n){
        int sum = 0;
        for (int i = 2; i <= n; i++){
            if (prime[i]){
                sum++;
            }
        }
        cout << sum << endl;
    }
    return 0;
}