/* 
 * File:   main.cpp
 * Author: virtualdemon
 *
 * Created on April 27, 2010, 4:44 PM
 */
#include <cstdlib>
#include <fstream>
#define Nmax 2000000/16+1

/*
 * 
 */
using namespace std;
char is_prime[Nmax];
int main(int argc, char** argv)
{
    unsigned int N, i, j, pas;
    ifstream in( "ciur.in" );
    in>>N;
    for( i=1; ((i*i)<<1)+(i<<1) < N; ++i )
        if( ! ( is_prime[i>>3] & (1<<(i&7)) ) )
        {
            pas=(i<<1)+1;
            for( j=((i*i)<<1)+(i<<1); (j<<1) < N; j+=pas )
                is_prime[j>>3]|=(1<<(j&7));
        }
    for( j=i=1, N>>=1; i < N; ++i )
        if( ! ( is_prime[i>>3] & (1<<(i&7)) ) )
            ++j;
    ofstream out( "ciur.out" );
    out<<j<<'\n';
    return (EXIT_SUCCESS);
}