/* 
 * File:   main.cpp
 * Author: virtualdemon
 *
 * Created on March 18, 2010, 3:57 PM
 */
#include <fstream>

/*
 *
 */
using namespace std;
bool is_prime[ 2000010 ];
int main( void )
{
    int N, i, j, nr;
    ifstream in( "ciur.in" );
    in>>N;
    for( i=2; i*i <= N; ++i )
        if( false == is_prime[i] )
            for( j=i*i; j <= N; j+=i )
                is_prime[j]=true;
    for( nr=0, i=2; i <= N; ++i )
        if( false == is_prime[i] )
            ++nr;
    ofstream out( "ciur.out" );
    out<<nr;
    return 0;

}