#include<stdio.h>
#include<math.h>
using namespace std;

int n,tot;
char v[2000005];

int main()
{
int i,j;
freopen("ciur.in","r",stdin);
freopen("ciur.out","w",stdout);
scanf("%d",&n);
for(i=2;i<=n;i++)v[i]=1;
for(i=2;i<=n;i++)
    {
    if(v[i])
        {
        tot++;
        for(j=i+i;j<=n;j+=i)v[j]=0;
        }
    }
printf("%d",tot);
return 0;
}