#include<stdio.h>
  long int i,j,n,contor;
 char a[2000000];
int main()
{
 FILE *f,*g;
 f=fopen("ciur.in","r");g=fopen("ciur.out","w");
 fscanf(f,"%ld",&n);
 contor=n-1;
 for (i=2;i<=n;i++)
       if (a[i]==0)
         {  contor--;
         for (j=i+i;j<=n;j+=i)
            a[j]=1;
        }
  fprintf(g,"%ld",contor);
  fclose(f);fclose(g);
  return 0;
}