#include<stdio.h>
char c[2000001];
int ciur (int n)
{
	long int d=2,i,num;
	while (d*d<n)
	{
		if(!c[d])
		{
			for (i=d*d; i<=n; i+=d) 
			c[i]=1;
		}
		d++;
	}
	return 0;
}
int numere(int n)
{
	long int i,num=0;
	for (i=2; i<=n; ++i)
		if (!c[i]) num++;
	return num;
}
int main()
{
	long int n;
	freopen ("ciur.in","r",stdin);
	freopen ("ciur.out","w",stdout);
	scanf("%ld",&n);
	ciur(n);
	printf("%ld ",numere(n));
	return 0;
}