#include<fstream.h>
#define dim 20004
char ciur[dim];
long n,k;
ifstream f("ciur.in");
ofstream g("ciur.out");
int main()
{
 f>>n;
for (int i=2;i<=n;++i)
    ciur[i]=1;
for (i=2;i*i<=n;++i)
    if (ciur[i])
     for (int j=2;j<=n/i;j++)
       ciur[i*j] = 0;
for(i=2;i<=n;i++)
    if(ciur[i])
     k++;

     g<<k;

   f.close();
   g.close();
   return 0;
}