#include<stdio.h>
#include<string.h>
char v[2000005];
int main ()
 { long n,i,j,cant=0;
   FILE*f=fopen("ciur.in","r");
   FILE*g=fopen("ciur.out","w");
   fscanf(f,"%ld",&n);
   memset(v,'1',n);
   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;
   }