#include <iostream>
#include <fstream>
using namespace std;
int p[2000000];

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

    int nr,n;
    fin>>n;
    for (int i=2; i<=n; ++i){
        if (p[i]==0)
            ++nr;
        for (int j=i+i; j<=n; j+=i){
            p[j] = 1;
        }
    }
    fout<<nr;
    return 0;
}