#include<stdio.h>
char c[10000];
void ciur (int n)
{
	int d=2,i;
	c[0]=1; c[1]=1;
	while (d*d<n)
	{
		if(!c[d])
			for (i=d*d; i<=n; i=i+d) 
				c[i]=1;
		d++;
	}
}
int numere(int n)
{
	int i,num=0;
	for (i=2; i<=n; ++i)
		if (!c[i]) num++;
	return num;
}
main()
{
	int n;
	freopen ("ciur.in","r",stdin);
	freopen ("ciur.out","w",stdout);
	scanf("%d",&n);
	ciur(n);
	printf("%d ",numere(n));
}