#include <iostream>
#include <fstream>
#include <vector>
#include <cmath>

int main()
{
    std::ifstream in ( "ciur.in" );
    std::ofstream out ( "ciur.out" );
    int n;
    in >> n;

    std::vector<int> prim ( n + 1, 1 );
    int nr = 0;
    for( int i = 2; i <= sqrt( n ); i++ )
    {
        if( prim[i] )
        {
            nr++;
            for( int j = i * i; j <= n; j += i )
            {
                prim[j] = 0;
            }
        }
    }

    out << nr;
    in.close();
    out.close();
    return 0;
}