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

int n, nrprime, i, j;
unsigned char prim[2000005];

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

    scanf("%d", &n);
    for (i = 2; i <= n; i++)
    	prim[i] = 1;

    for (i = 2; i <= n; i++)
    	if (prim[i] == 1)
    	{
    		nrprime++;
    		for (j = i + i; j <= n; j = j + i)
    			prim[j] = 0;
    	}
    printf("%d\n", nrprime);
}