#include<cstdio>
char v[2000001];
int main()
{
 int n,s;
 freopen("ciur.in","r",stdin);
 freopen("ciur.out","w",stdout);
 scanf("%d",&n);
 v[1]=1;
 for(int i=2;i*i<=n;i++)
    {
     for(int j=i+i;j<=n;j+=i)
        {
         v[j]=1;
        }
    }
 s=0;
 for(int i=1;i<=n;i++)
    {
     if(v[i]==0)
        s++;
    }
 printf("%d",s);
return 0;
}