#include <stdio.h>
#include <stdbool.h>
#define VM 2000001

bool c [VM];

int main()
{
    freopen("ciur.in", "r", stdin);
    freopen("ciur.out", "w", stdout);
    int i, j, n, nr = 0;
    for (i = 2; i * i < VM; i ++)
    {
        if (! c [i])
        {
            for (j = i * i; j < VM; j += i)
            {
                c [j] = true;
            }
        }
    }
    scanf ("%d", &n);
    for (i = 2; i <= n; i ++)
    {
        if (!c [i])
        {
            //printf ("%d ", i);
            nr++;
        }
    }
    printf("%d", nr);
    return 0;
}