#include<stdio.h>
#define nmax 2000005
int i,j,k,n,w[1025],p;
char v[nmax];

int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);

	scanf("%d",&n);

	v[1]=-1;

	for(i=2;i<=n;i++)
		if(v[i]==0)
		{
			k++;

			for(j=i+i;j<=n;j+=i)
				v[j]=-1;

		}
	printf("%d\n",k);
	/*
	for(i=n;i>0 && p<1000;i--)
		if(v[i]==0)
			w[++p]=i;

	for(i=p;i>0;i--)
		printf("%d ",w[i]);
	*/
	return 0;
}