#include<iostream>
#include<stdio.h>
using namespace std;
int n,tot;
int p[100000005];
bool vis[100000005];
int main(){
	scanf("%d",&n);
	for(int i=2;i<=n;i++){
		if(!vis[i])
			p[++tot]=i;
		for(int j=1;j<=tot&&i*j<=n;j++){
			vis[p[j]*i]=1;
			if(i%p[j]==0)
				break;
		}
	}
	printf("%d",tot);
}