#include <bits/stdc++.h>
using namespace std;

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

int n, cont;
bool f[2000005];

int main()
{

    in>>n;

    for( int i = 1; i <= n; i++ )
        f[i] = true;


    for( int i = 2; i <= n; i++ )
        if( f[i] )
        {
            cont++;

            for( int j = 2; i*j <= n ; j++ )
                f[i*j] = 0;
        }


    out<<cont;

    return 0;
}