#include<stdio.h>
  long int n,i,j,contor;
 char a[20000];
int main()
{

 FILE *f,*g;
 f=fopen("ciur.in","r");g=fopen("ciur.out","w");
 fscanf(f,"%ld",&n);
 contor=1;
 for (i=2;i<=n;i++)
    a[i]=1;
 for (i=2;i<=n;i++)
       if (a[i]==1)
         {  contor++;
         for (j=i+i;j<=n;j=j+i)
            a[j]=0;
         }
  fprintf(g,"%ld",contor);
  fclose(f);fclose(g);
  return 0;
}