#include <bits/stdc++.h>
using namespace std;
int Ld[2000013],Q[2000013],sol(0),n,sf(0);

int main()
{
 ifstream cin("ciur.in");
 ofstream cout("ciur.out");
 cin>>n;
 for (int i=2;i<=n;++i)
	{
	 if (Ld[i]==0) 
	      {
		  Ld[i]=i; 
		  Q[++sf]=i;
	      }
	 for (int j=1;j<=sf && i*Q[j]<=n && Q[j]<=Ld[i] ; ++j)
	   Ld[i*Q[j]]=Q[j];
	}
 for (int i=2;i<=n;++i) 
    if (Ld[i]==i) ++sol;
 cout<<sol;
 return 0;
}