#include <cstdio>

using namespace std;

int nr,n,prim[1000000],x,i;
bool ok;

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

    scanf("%d", &n);

    prim[1]=2; nr=1;
    for (x=3;x<=n;x+=2)
     {
         ok=true;
         for (i=1;i<=nr && prim[i]*prim[i]<=x;i++)
          if (x%prim[i]==0)
            ok=false;
          if (ok)
            prim[++nr]=x;
     }

   printf("%d", nr);

    return 0;
}