#include<fstream.h>
int ok[10000];
int main()
{unsigned long n,i,j,k=1;

ifstream f("ciur.in");
ofstream g("ciur.out");

f>>n;

for(i=3;i<=n;i+=2)
   if(ok[i]==0)
     {k++;
      for(j=2*i;j<=n;j+=i)
	  ok[j]=1;
      }

g<<k<<'\n';

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