#include <stdio.h>
#include <math.h>


unsigned long prim (unsigned long a) {
	unsigned long ok, d;
	ok = 1;
	d = 2;
	while (d <= a/2) {
		if (a % d == 0) ok = 0;
		d++;
	}
	return ok;
}

int main () {

	FILE *f, *g;
	unsigned long N, nr, i;
	f = fopen("ciur.in", "r");
	g = fopen("ciur.out", "w");
	fscanf(f, "%lu", &N);
	nr = 0;
	for (i = 2; i <= N; i++) {
		if (prim(i)) nr++;
	}
	
	fprintf(g, "%lu", nr);
	
	return 0;
}