#include<cstdio>

char a[2000001];
int n,i,j,k;

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