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