#include <iostream>
#include <fstream>
#include <bits/stdc++.h>

using namespace std;

ifstream in("ciur.in");
ofstream out("ciur.out");

int main()
{
    //int n = (cin >> (cout << "", n), n);
    int n;
    in >> n;

    bool a[n+1];
    memset(a, true, sizeof(a));

    for(int i = 2; i*i<=n;++i){
        if(a[i] == true){
            for(int j = i*2; j <= n; j += i){
                a[j] = false;
            }
        }
    }

    int prime = 0;

    for(int i = 2; i<=n;++i){
        if(a[i]){
            ++prime;
        }
    }

    out << prime;
}