#include <iostream>
#include <fstream>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
char a[2000005];
int n,i,j,nr;
int main()
{
   f>>n; for(i=2;i<=n;i++)a[i]=0;
   for(i=2;i<=n;i+=2)a[i]=1; nr=1;
   for(i=3;i<=n;i+=2)
          if(a[i]==0)
              { nr++; for(j=i*2;j<=n;j+=i)a[j]=1;}
   g<<nr;
    return 0;
}