#include <stdio.h>

char prim[2000005];

int main()
{
  int i,n,count=0;
 FILE *f=fopen("ciur.in","r");
 FILE *g=fopen("ciur.out","w");

fscanf(f,"%d",&n);


 for(i=1;i<=n;i++)
 {
   prim[i]=1;
 }

 for  (i=2;i<=n;i++)
 {

   if (prim[i])
   {
    int j;
     for (j=2*i;j<=n;j+=i)
     {
      prim[j]=0;
     }
    count++;
   }

 }
fprintf(g,"%d",count);

fclose(f);fclose(g);
return 0;
}