#include<fstream>
#define IN "ciur.in"
#define OUT "ciur.out"
#define MAX 2000001

using namespace std;

ifstream fin(IN);
ofstream fout(OUT);

bool v[MAX];

int n, sol=1, i, j;

void ciur();

int main()
{
	ciur();
	return 0;
}

void ciur()
{
	fin>>n;
	/*for(i=3; i<=n; i+=2)
		v[i]=1;*/
	for(i=3; i<=n; i+=2)
		if(!(v[i]))
		{
			sol++;
			for(j=i+i; j<=n; j+=i)
				v[j]=1;
		}
	fout<<sol<<'\n';
}