#include<cstdio>

char a[1000000];
int n,i,j,k;

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