#include <fstream>
#include <cstdlib>
#define N_MAX 2000011

using namespace std;

char isPrime[N_MAX];

int main()
{
	int N, i, j, count;
	ifstream in( "ciur.in" );
	ofstream out( "ciur.out" );

	in>>N;	
	for( i=1; ((i*i)<<1) + (i<<1) < N; ++i )
		if( false == ( isPrime[i>>3] & (1<<(i&7)) ) )
		{
			count=(i<<1)+1;
			for( j=((i*i)<<1)+(i<<1); (j<<1) < N; j+=count )
				isPrime[j>>3]|=1<<(j&7);
		}
	for( count=1, i=1, j=3; j <= N; ++i, j+=2 )
		if( false == ( isPrime[i>>3] & (1<<(i&7)) ) )
			++count;

	out<<count<<'\n';

	return EXIT_SUCCESS;
}