// Sieve of Eratosthenes.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include "stdio.h"

int a[20000001], N, c=0;

int main () {
	freopen("ciur.in", "r", stdin);
	freopen("ciur.out", "w", stdout);

	scanf("%d", &N);

	for (int i = 2; i <= N; ++i) {
		if (!a[i]) {
			++c;
			for (int j = i*2; j < N; j+=i) {
				a[j]=1;
			}
		}
	}
	printf("%d", c);

	return 0;
}