#include <fstream>
#include<stdio.h>

using namespace std;

long ciur (long k)
{
	long s=1,a[10000],i,j;
	a[2]=1;
	for (i=3;i<=k;i+=2)
	{
		a[i]=1;
		a[i+1]=0;
	}
	for (i=3;i<=k;i++)
	{
		while (!a[i])i++;
		s++;
		for (j=i*i;j<=k;j+=i)
			a[j]=0;
		i++;
	}
	return s;
}

int main()
{
	long x,n;
	ifstream f ("ciur.in");
	freopen("ciur.out","w",stdout);
	f>>n;
	x=ciur(n);
	printf("%d\n",x);
}