program ciur;
var a: array[2..2000000] of 0..1;
n,i,p,j: longint;
f: text;
begin
     assign(f,'ciur.in');
     reset(f); read(f,n); close(f);
     for i:=2 to n do
          if a[i]=0 then
          begin
               inc(p);
               j:=i;
               repeat
                     a[j]:=1;
                     j:=j+i;
               until j>n;

          end;
     assign(f,'ciur.out');
     rewrite(f);
     write(f,p);
     close(f);
end.