#include<cstdio>
#include<bitset>
using namespace std;
int t,n;
bitset <2000001>s;
void ciur()
{
    int i,j;
    t=1;
   for (i=1;(i<<1)+1<=n;i+=1)
   {
       if(s[i]==0)
       {
           ++t;
           for (j=3*i+1;(j<<1)+1<=n;j+=(i<<1)+1)
            s[j]=1;
       }
   }
}
int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    ciur();
    printf("%d",t);
return 0;
}