#include<stdio.h>
int t,i,n,j,cnt;
bool a[2000005];
int main(){
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%d",&n);
	t=n;
	cnt=0;
	for (i=1; i<=n; i++) 
		a[i]=true;
	for (i=2; i<=n; i++){
		if (a[i]==true){
			cnt++;
			for (j=i+i; j<=n; j+=i) a[j]=false;
		}
	}
	printf("%d",cnt);
	return(0);
}