///1 ≤ n ≤ 10 000
///v[n]≤ 2.000.000.000.
#include <bits/stdc++.h>
#include <fstream>

using namespace std;
ifstream fin("problemeclasa.in");
ofstream fout("problemeclasa.out");

bool c[2000000];
int n=1,cont=0;

void cera(){
    for(int i=2;i<=n;i++){
        if(!c[i]){
            for(int j=2;j*i<=n;j++) c[i*j]=1;
            cont++;
        }
    }
}

int main(){
    fin>>n;
    cera();
    fout<<cont;
}