#include<stdio.h>
#include<math.h>
#define  NM 2000000
int main()
{
    char v[NM+1]={0};
    int i,j,n,p,poq;
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    v[1]=1;
    poq=sqrt(n);
    for(i=2;i<=poq;i++)
                       if(v[i]==0)
                                  for(j=2;j*i<=n;j++)
                                                     v[i*j]=1;
    p=0;
    for(i=1;i<=n;i++) if(v[i]==0) p++;
    printf("%d",p);
    return 0;
}