#include <iostream>
#include <vector>
#include <fstream>

using namespace std;

bool a[2000005];
int n, cou;
ifstream fin("ciur.in"); ofstream fout("ciur.out");

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

int main(){
    fin >> n;
    sieve();
    fout << cou << endl;
}