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

using namespace std;

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

int main(){
    int n;
    f >> n;
    std::vector<bool> nonprim(2000001,false);
    nonprim[1] = true;
    nonprim[2] = false;
    int nrprim = 0;
    unsigned i, j;
    for (i=2; i<=n; i++){
        if (!nonprim[i]){
            nrprim++;
            for (j=i*i; j<=n; j+=i) nonprim[j] = true;

        }
    }
    g << nrprim;
}