#include <fstream>
using namespace std;
#include <vector>

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

int N;
vector <bool> v ( 2000000 );

void ciur ( int N )
{
	int cnt = 0;
	
	for ( int i = 1; i <= N; ++i )
		v [ i ] = true;
	for ( int i = 2; i <= N; ++i )
		if ( v [ i ] )
		{
			++cnt;
			for ( int j = i + i; j <= N; j += i )
				v [ j ] = false;
		}
		
	out << cnt;
}

int main ()
{
	in >> N;
	
	ciur ( N );
	
	return 0;
}