#include <stdio.h>

using namespace std;
int N,nr;
char sel[2000001];

int main()
{
int i,j;

  freopen("ciur.in","r",stdin);
  freopen("ciur.out","w",stdout);
 scanf("%d",&N);

 for(i=2;i<=N;++i)
    sel[i]=1;
  for (i=2;i<=N;++i)
    { if (sel[i])
       nr++;
       for (j=i+i;j<=N;j+=i)
         sel[j]=0;
    }

    printf("%d",nr);



   return 0;
}