/* ciurul lui eratosthene */
#include<stdio.h>
#include<math.h>
FILE *f=fopen("ciur.in","r");
FILE *g=fopen("ciur.out","w");
long n;
char viz[2000001];
int main()
{
 fscanf(f,"%ld",&n);

  long i,k;
 
  k=0;
   for(i=2;i<=n;i++)
   {
   if(!viz[i])
      {++k;
    
    for(long j=i+i;j<=n;j+=i)
       viz[j]=1;}
   
	 }


  fprintf(g,"%ld",k);
fcloseall();

return 0;
}