#include<stdio.h>
long n,k;
long a[2000005];
int main()
{
	long i,j;
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	scanf("%ld",&n);
	/*a=new char[n+2];*/
	for(i=2;i<=n;++i)
		a[i]=1;
	for(i=1;i<=n;++i)
		if(a[i]==1){
			k++;
			for(j=i+i;j<=n;j+=i)
				a[j]=0;
		}
	printf("%ld\n",k);
	return 0;
}