#include <iostream>
#include <cstdio>
#include <algorithm>
#include <string>

using namespace std;

#define maxN 2000010

bool cont[maxN];
int k;


void ciur (int X)
{
	if (X < 2) return;
	k = 1;
	
	for (int i = 3; i <= X; i += 2)
	{
		if (cont[i]) continue;
		
		++ k;
		
		for (int j = i + i; j <= X; j += i) cont[j] = true;
	}
}


int main()
{
	freopen ("ciur.in", "r", stdin);
	freopen ("ciur.out", "w", stdout);
	
	int N;
	
	scanf ("%d", &N);
	
	ciur (N);
	
	printf ("%d", k);
	
	return 0;
}