#include <stdio.h>
#define nmax 2000008

char p[nmax];
int i, n, j, h;

int main()
{
    freopen("ciur.in", "rt", stdin);
    freopen("ciur.out", "wt", stdout);

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

    for (i = 2; i <= n; ++i)
	if (p[i])
	{
	    ++h;
	    for (j = i + i; j <= n; j += i)
	    p[j] = 0;
	}

    printf("%i\n", h);
}