#include <fstream.h>

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


unsigned long n, i, j, c;
int sw;

int main()
{

	fin >> n;

	for( i = 2; i <= n; i++ )
	   {
		  sw = 1;
		  for( j = 2; j <=(i/2); j++ )
			  if( i % j == 0 )
				{
					sw = 0;
					break;
				}

		  if(sw)  c++;

	   }


	fout << c;
    fout.close();

 return 0;
}