#include <fstream.h>

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



unsigned char a[32000];

int main()
{

	unsigned long n, i, c, j;

	fin >> n;


	for( i = 2; i <= n; i++ )
	   {
		 if(!a[i])
		 {
		  c++;

		  for( j = i+i; j <=n; j += i )
			a[j] = 1;

		 }
	   }

	fout << c;
    fout.close();

 return 0;
}