#include <iostream>
#include <fstream>
using namespace std;
ifstream fin ("ciur.in");
ofstream fout ("ciur.out");
int i,a[300000005],k,j,n;
int main()
{
    fin >> n;
    for (i=1;i<n;i++)
        a[i]=i++;
    k=1;
    for (i=3;i<=n;i=i+2)
         if (a[i]!=0)
          {k++;
           for (j=2*i;j<=n;j+=i)
             a[j]=0;
          }
   fout << k;

    return 0;
}