#include <stdio.h>
#include <stdlib.h>

FILE *f = fopen("ciur.in", "r");
FILE *g = fopen("ciur.out", "w");

int main() {
	int *v, n, nr = 0;
	fscanf(f,"%d", &n);
	v = (int*)calloc(n + 1, sizeof(int));
	v[0] = v[1] = 1;
	for (int i = 2; i <= n; i++) 
		if (!v[i]) { 
		nr++;
		for (int j = 2 * i; j <= n; j += i)
			v[j] = 1;
		}
	fprintf(g,"%d", nr);
	return 0;
}