#include <cstdio>
#include <bitset>

using namespace std;

int n, i, j, sol;
bitset <2000001> c;

int main ()
{
    freopen ("ciur.in", "r", stdin);
    freopen ("ciur.out", "w", stdout);
    scanf ("%d", &n);
    for (i=2; i<=n; i++) c[i]=1;
    for (i=2; i<=n; i++)
    {
        if (c[i])
        {
            sol++;
            for (j=i+i; j<=n; j+=i) c[j]=0;
        }
    }
    printf ("%d", sol);
}