#include <cstdio>

using namespace std;

int n, nr;
bool a[2000002];

void ciur()
{
    for (int i=2; i<=n; ++i)
        if (!a[i])
        {
            ++nr;
            for (int j=i<<1; j<=n; j+=i)
                a[j]=true;
        }
}

int main()
{
    freopen ("ciur.in","r",stdin);
    freopen ("ciur.out","w",stdout);
    scanf ("%d",&n);
    ciur();
    printf("%d\n",nr);
    return 0;
}