#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
int nr,i,j,p[2000000/2+1],n;
int main()
{
    fin>>n;
    nr=1;
  for (i=1;2*i*i+2*i<=n;i++)
    if (p[i]==0)
      for (j=2*i*i+2*i;2*j+1<=n;j+=2*i+1)
        p[j] = 1;
  for (i=1;2*i+1<=n;i++)
      if (p[i]==0) nr++;
      fout<<nr;
    return 0;
}