#include <cstdio>
using namespace std;
bool a[2000001];
int i ,n, j, nr;
int main()
    {
        freopen("ciur.in","r",stdin);
        freopen("ciur.out","w",stdout);
        scanf("%d",&n);
        a[0]=true;
        a[1]=true;
        for (i=1;i<=n;i++)
        {
            if (a[i]==false)
               {
                   for (j=2;j<=n/i;j++) a[j*i]=true;
               }
        }
        for (i=1;i<=n;i++) if (a[i]==false) nr++;
        printf("%d",nr);
    }