#include <iostream>
#include <fstream>
#include <map>
#include <vector>
#include <list>
#include <iterator>
#include <queue>
#include <algorithm>
#include <tuple>

using namespace std;

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

int main(){

    int N;
    in >> N;

    vector <bool> ciur(N + 1);

    for(int i = 2; i <= N; i++){
        if(!ciur[i]){
            for(int j = i + i; j <= N; j += i)
                ciur[j] = true;
        }
    }
    out << count(ciur.begin() + 2, ciur.end(), 0);

    return 0;
}