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