#include <cstdio>
#define DIM 2000005
int e[DIM];

int ciur(int n)
{
	e[0] = e[1] = 1;
	int i, j;
	for (i = 1; i * i<= n; i++)
		if (e[i] == 0)
			for (j = 2 * i; j <= n; j += i)
				e[j] = 1;

	int nr = 0;
	for (i = 1; i <= n; i++)
		if (e[i] == 0)
			nr++;

	return nr;
}


int main()
{
	FILE *f = fopen("ciur.in", "r");
	int n;
	fscanf(f, "%d", &n);
	fclose(f);

	f = fopen ("ciur.out", "w");
	printf(f, "%d\n", ciur(n));
	fclose(f);
	return 0;
}