#include <cstdio>

using namespace std;

char ciur [2000001];

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

    int i,j,n,nr=0;

    scanf ("%d",&n);

    for (i=2; i*i<=n; i++)
    {
        if (ciur[i]==0)
        {
            for (j=2*i; j<=n; j+=i)
            {
                ciur[j]=1;
            }
        }
    }

    for (i=2; i<=n; i++)
    {
        if (ciur[i]==0)
        {
            nr++;
        }
    }

    printf ("%d\n",nr);

    return 0;
}