#include<fstream>
#include<math.h>

using namespace std;

ifstream in("ciur.in");
ofstream out("ciur.out");

int i,n,nr,j,ok[2000001];

int ciur()
{
	i=2;
	while (i<=(int)sqrt((float)n))
	{
		if (!ok[i])
			for (j=i*2;j<=n;j+=i)
				ok[j]=1;
		i++;
	}
	
	for (i=2;i<=n;i++) 
		if (!ok[i]) nr++;
	return nr;
}

int main()
{
	in>>n;
	
	out<<ciur();
}