#include <cstdio>
#define N 2000010
using namespace std;
int a[N],p,j,q,n,nr;
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    for(int i=2;i<=n;i++)
    {
        if(a[i]==0)
        {
            nr++;
            j=i;
            q=i;
        }
        for(;j<=n;j+=q)
            a[j]=1;
    }
    printf("%d\n",nr);
    return 0;
}