#include<fstream>
using namespace std;
int v[2000000];
int main()
{unsigned long n,k,i,j;
 ifstream f("ciur.in");
 ofstream g("ciur.out");

 f>>n; k=1;
	for(i=3;i<=n;i+=2)
		if(v[i]==0)
		  {k++;
		   for(j=i;j<=n;j+=i)
				v[j]=1;//,k++;
		   }
 //for(i=2;i<=n;i++)if (v[i]==0)k++;			
 g<<k<<'\n';
 f.close();
 g.close();
 return 0;
}