#include<stdio.h>
#define N 2000001
int n,nr,c,sol[2001];
bool p[N];
void ciur(int n)
{
	int i,j;
	for(i=2;i<=n;i++)
		p[i]=1;
	for(i=2;i<=n;i++)
		if(p[i])
		{
			nr++;
			for(j=i+i;j<=n;j+=i)
				p[j]=0;
		}
}
int main()
{
	freopen("ciur.in","r",stdin);
	freopen("ciur.out","w",stdout);
	//int i;
	scanf("%d",&n);
	ciur(n);
	printf("%d\n",nr);
	/*for(i=n;i>1;i--)
	{
		if(p[i])
			sol[++c]=i;
		if(c==1000)
			break;
	}
	for(i=c;i>1;i--)
		printf("%d ",sol[i]);
	printf("%d\n",sol[1]);*/
	return 0;
}