//#include "stdafx.h"
#include<iostream>
#include<stdio.h>

using namespace std;

int n, nr=0;
char prim[2000001];

int main()
{
	freopen("ciur.in", "r", stdin);
	freopen("ciur.out", "w", stdout);
	scanf("%d", &n);
	for (int i = 2; i <= n; i++)
		prim[i] = 1;
	for (int i = 2; i <= n; i++)
	{
		if (prim[i]==1)
		{
			int j = i;
			while (j <= n)
			{
				prim[j] = 0;
				j = j + i;
			}
			nr++;
		}
	}
	printf("%d", nr);
	return 0;

}