#include <fstream>

using namespace std;

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

int n, sol;
char prim[2000005];

int main()
{
    int i, j;
    f>>n;
    for (int i=2; i<=n; ++i) prim[i] = 1;
    for (int i=2; i<=n; ++i)
      if (prim[i])
      {
          ++sol;
          for (int j=i+i; j<=n; j+=i) prim[j]=0;
      }
    g<<sol<<'\n';
    f.close(); g.close();
    return 0;
}