#include<iostream>
#include<fstream>
#include<cstring>
#define lmax 2000000
using namespace std;
ifstream f("ciur.in",fstream::in);
ofstream g("ciur.out",fstream::out);
bool viz[lmax];
unsigned int n,m,lol,i,contor,j;
int main()
{f>>n;
 for(i=2;i<=n;i++)
	  if(!viz[i])
	  { for(j=i+i;j<=n;j+=i)
		   viz[j]=1;
	    contor+=1;
	  }
g<<contor;
f.close();
g.close();
return 0;
}