#include <iostream>
#include <fstream>

using namespace std;

const int nm = 2000000;

int main()
{
  int n,i,j,nr=1;
  int v[nm];
    ifstream f1;
    ofstream f2;
    f1.open("ciur.in");
    f2.open("ciur.out");

    f1 >> n;
    f1.close();

    for(i=3;i<=n;i+=2)
    {
      if (v[i]==0)
        {
           nr++;
            for(j=i+i;j<=n;j+=i)
            {
                v[j]=1;
            }
        }
    }
    f2 << nr;
    f2.close();

  return 0;

}