#include <iostream>
#include <fstream>

using namespace std;

int v[2000005];

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

	int n, s = 0, i, j;
	f >> n;

	for (i = 2; i <= n; ++i){
		if (v[i] == 0){
			s++;
			for (j = i + i; j <= n; j += i)
				v[j]=1;
		}
	}

	g << s;

	f.close();
	g.close();
	return 0;
}