#include <fstream>
#include <iostream>
#include <vector>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");

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

		}
	}
	g << nrprim;
	//cout << nrprim;
}