#include <fstream>
#include <cstdlib>
#define N_MAX 2000000/16+1

using namespace std;
char isPrime[N_MAX];
int main( void )
{
	int N, i, j, c;
	ifstream in( "ciur.in" );
	in>>N;
	for( i=1; ((i*i)<<1) + (i<<1) < N; ++i )
		if( 0 == ( isPrime[i>>3] & (1<<(i&7)) ) )
		{
			c=(i<<1)+1;
			for( j=((i*i)<<1)+(i<<1); (j<<1) < N; j+=c )
				isPrime[j>>3]|=(1<<(j&7));
		}
	for( i=1, j=1; (j<<1)+1 <= N; ++j )
		if( 0 == ( isPrime[j>>3] & (1<<(j&7)) ) )
			++i;
	ofstream out( "ciur.out" );
	out<<i<<'\n';
	return EXIT_SUCCESS;
}