#include <cstdio>
using namespace std;
long n,i,j,cate,a[2000002];
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    for(i=2;i<=n;i++)
        a[i]=1;
    for(i=2;i<=n;i++)
        {
            if(a[i]==1)
            {
                cate++;
                for(j=i+i;j<=n;j=j+i)
                    a[j]=0;
            }
        }
    printf("%d\n",cate);
    return 0;
}