#include <iostream>
#include <fstream>

using namespace std;

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

char a[2000001];
int n, nr;

int main()
{
    int i, j;

    f>>n;

    for (i=2; i<=n; i++) a[i]='t';

    for (i=2; i<=n; i++)
      if (a[i]=='t')
      {
          //cout<<i<<" "; pt a afisa toti factorii primi
          nr++;
          for (j=2; j<=n/i; j++)
            a[j*i]='f';
      }
    g<<nr;
    return 0;
}