#include<fstream>
using namespace std;
bool a[10000];
ifstream f("ciur.in");
ofstream h("ciur.out");
int main()
{
	int n, i, j, np;
    
		f >> n;
		np = 0;
		a[1] = 1;
	for ( i = 2; i <= n; i++)
		if ( a[i] == 0 )
		{
			np=np+1;
			j = 2 * i;
		while (j <= n)
		{
			a[j] = 1;
		    j = j + i;
		}
		}

  h << np << endl;
  f.close();
  h.close();
return 0;
}