#include <iostream>
#include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int n,a[2000000],i,j,nr;
int main()
{
   f>>n;
   for(i=2;i<=n;i+=2)a[i]=1;
   for(i=3;i<=n/2;i+=2)
          if(a[i]==0)
              for(j=i*2;j<=n;j+=2)a[j]=1;
   for(i=2;i<=n;i++)
       if(a[i]==0)nr++;
   g<<nr;
    return 0;
}