#include<fstream>
#include<iostream>

using namespace std;
ifstream in ("ciur.in");
ofstream out ("ciur.out");
int main ()
{
    int n, i, j;
    bool a[2000003];
    in >> n;

    for (i=3; i<=n; i=i+2)
            a[i] = 1;

    for (i=3; i<=n; i=i+2)
    {
        if (a[i])
        for (j=i*2; j<=n; j=j+i)
            a[j] = 0;
    }
    int cnt = 1;
    for (i=3; i<=n; i=i+2)
            if (a[i] == 1) cnt ++;

  /*  for (i=3; i<=n; i=i+2)
        if (a[i])
           cout << i << endl;
  */

    out << cnt;

    return 0;
}