#include <cstdio>
#include <bitset>
using namespace std;

bitset <2000001> v;
int N,cnt;

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

    scanf ("%d",&N);

    for (int i=2; i<=N; ++i)
        if (!v[i])
        {
            ++cnt;
            for (int j=i+i; j<=N; j+=i)
                v[j]=1;
        }

    printf ("%d",cnt);
    return 0;
}