#include<stdio.h>
#define Nmax 20000
int main()
{
  int n,k=0,i,j;
 int a[Nmax];
 FILE *f=fopen("ciur.in","r");
 FILE *g=fopen("ciur.out","w");
 fscanf(f,"%d",&n);
 for (i=2;i<=n;i++)
    a[i]=1;
 for (i=2;i<=n;i++)
      if (a[i]==1)
        {
         k++;
         for (j=2*i;j<=n;j=j+i)
            a[j]=0;
         }
  fprintf(g,"%d",k);
  fclose(f);fclose(g);
  return 0;
}