#include<stdio.h>

int main ()
 { long n,i,j,cant=0;
   char v[2000005];
   FILE*f=fopen("ciur.in","r");
   FILE*g=fopen("ciur.out","w");
   fscanf(f,"%ld",&n);
   for (i=2;i<=n;++i)
     v[i]=1;
   for (i=2;i<=n;++i)
     { if (v[i]==1)
           ++cant;

       for (j=i+i;j<=n;j+=i)
	  v[j]=0;
       }
   fprintf(g,"%ld\n",cant);
   fcloseall();
   return 0;
   }