#include <fstream.h>

int prim( long k );
long n, nr, i;

int main()
{
	ifstream fin("ciur.in");
	fin >> n;
	fin.close();
	for( i = 2; i <= n; i++ )
		if( prim( i ) )nr++;
	ofstream fout("ciur.out");
	fout << nr;
	fout.close():
	return 0;
}

int prim( long k )
{
	if( x == 2 || x == 3 || x == 5 || x == 7 || x == 11 || x == 13 || x == 17 || x == 19 ) return 1;
	for( int j = 2; j * j <= k; j++ )
		if( k % j == 0 )
			return 0;
	return 1;
}