#include <cstdio>

using namespace std;
int i,aux,n,b,k,j,p,m,s,cont;
short v[2000001];

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

    scanf("%d",&n);
    for(i=2;i<=n;i++)
    {
        i++;
        if(v[i]==0)
        {
            cont++;
            for(j=i;j<=n/i;j++)
            {
                v[i*j]=1;
                j++;
            }
        }

    }

    printf("%hd\n",cont);

}