/* 
 * File:   main.cpp
 * Author: virtualdemon
 *
 * Created on April 27, 2010, 4:33 PM
 */
#include <cstdlib>
#include <fstream>
#define Nmax 2000011

/*
 * 
 */
using namespace std;
bool is_prime[Nmax];
int main(int argc, char** argv)
{
    int N, nr=0, i, j;
    ifstream in( "ciur.in" );
    in>>N;
    for( i=2; i <= N; ++i )
        if( !is_prime[i] )
        {
            for( j=i*i; j <= N; j+=i )
                is_prime[j]=true;
            ++nr;
        }
    ofstream out( "ciur.out" );
    out<<nr<<'\n';
    return (EXIT_SUCCESS);
}