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

using namespace std;

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

#define NMax 2000010

int n;
vector<bool> prim(NMax, false);
int nrp;

int main(){
	int i, j;
	fin >> n;
	for(i = 2; i <= n; i++) prim[i] = true;
	for(i = 2; i <= n; i++){
		if(prim[i]){
			nrp++;
			for(j = i + i; j <= n; j += i) prim[j] = false;
		}
	}
	fout << nrp;
}