#include <fstream.h>
#include <stdlib.h>
#include <iostream.h>


ifstream  f("ciur.in");
ofstream g("ciur.out");
long int i,n,j,l,k=1;
bool *v;
int main ()
{f>>n;
if (n%2==0)
   n/=2;
else
   n=n/2+1;
v=(bool*)calloc(n+1,1);
for (j=2; j<=n; j++)
    if (v[j]==0)
    {i=2*j-1;
    for (l=j+i; l<=n; l+=i)
        v[l]=1;
    k++;}
g<<k;
f.close();
g.close();
return 0;}