#include <iostream>
#include <fstream>

using namespace std;

bool v[ 2000001 ];

void ciur ( int x )
{
    int i, j;

    for ( i=3; i*i<=x; i+=2 )
        if( v[i] == 0 )
           for ( j=i*i; j<=x; j+=i )
              v[j] = 1;
}

ifstream f ("ciur.in");
ofstream g ("ciur.out");

int main()
{
    int ct=0, n;

    f>>n;
    ciur ( n );

    if( n>=2 )
        ct++;

    for( int i=3; i<=n; i+=2 )
        if( v[i] == 0 )
          ct++;
    g<<ct;
    return 0;

}