#include<fstream>
using namespace std;

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

int prim( int n );

int main()
{
	int k = 0;
	long long n;
	fin >> n;
	for ( int j = 2; j <= n; j++ )
		if ( prim(j)  )
		k++;
		fout << k;

}

int prim(  int n )
{
	if( n == 2 )
		return 1;
	if ( n % 2 == 0 )
		return 0;
	for ( int d  = 3; d <= n / 2; d++ )
		if ( n % d == 0 )
			return 0;
		return 1;
}