#include <cstdio>

using namespace std;

int n;
char prim[2000001];

int main () {
	freopen ("ciur.in", "r", stdin);
	scanf ("%d", &n);
	fclose (stdin);
	int i, j, nr=0;
	for (i=2; i<=n; ++i) 
		if (prim[i] == 0) {
			++nr;
			for (j=i+i; j<=n; j+=i)
				prim[j] = 1;
		}
	freopen ("ciur.out", "w", stdout);
	printf ("%d", nr);
	fclose (stdout);
	return 0;
}