#include<iostream>
#include<fstream>
using namespace std;
int main(){

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

    int n;
    fin>>n;
    int v[n],suma=0;
    for(int i=1;i<=n;++i){

        v[i]=0;
    }

    for(int i=2;i<=n;++i){

        if(v[i]==1)continue;

        suma++;
        for(int j=2;j<=n;++j){

            if(i*j>n)break;v[i*j]=1;
        }
    }

    fout<<suma;
}