#include <iostream>
#include <fstream>
#include <string.h>
#define nmax 2000005
using namespace std;

bool prim[nmax];
int n;
int main() {
	ifstream f("ciur.in");
	ofstream g("ciur.out");

	f>>n;

	for(int i = 2; i <= n; i++) prim[i] = true;

	for(int i = 2; i*i <= n; i++) {
		if(prim[i]) 
			for(int j = 2*i; j <= n; j += i) prim[j] = false;
	}

	int sol = 0;
	for(int i=2; i<=n; i++) sol += prim[i];

	g<<sol<<"\n";
	return 0;
}