#include <cstdio>

using namespace std;

int n;
bool prim[2000010];

int ciur(int n)
 {
     int cnt=0;
     for (int i=2;i<=n;i++) prim[i]=true;
     for (int i=2;i<=n;i++)
      if (prim[i])
       {
           for (int j=i*i;j<=n;j+=i) prim[j]=false;
           cnt++;
       }
     return cnt;
 }



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

    scanf("%d", &n);

    printf("%d", ciur(n));

    return 0;
}