#include <fstream.h>
#include <string.h>

int main()
{
 long n,i,j,prime;
 int v[2000002];

 ifstream fin("ciur.in");
 ofstream fout("ciur.out");

 fin>>n;
 prime=n-1;

 memset (v,0,sizeof(v));

 for (i=2; i<=n; i++)
	if (v[i]==0)
	 for (j=2; j<=n/i; j++)
		{
		 if (v[i*j]==0)
			{
			 v[i*j]=1;
			 prime--;
			}
		}

 fout<<prime<<'\n';

 fin.close();
 fout.close();

 return 0;
}