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


int main () {

int n, count = 0, i, j;

freopen ("ciur.in", "r", stdin);
freopen ("ciur.out", "w", stdout);

scanf ("%d", &n);
char *num = (char*) calloc (n + 1, sizeof(char));

int step = 1;
for (i = 2; i <= n; i += step)
	if (!num[i])
	{
		count ++;
		num [i] = 1;
		for (j = i * i; j <= n; j += i)
			num[j] = 1;
		if (i == 3)
			step ++;
	}
printf ("%d", count);
return 0;
}