program erac;
var n,cont:0..2000000;
    i,j:0..4000000;
    a:array[0..2000000]of boolean;
    t:text;
begin
 assign(t,'ciur.in'); reset(t);
 readln(t,n);
 close(t);

 for i:=4 to n do a[i]:=false;

 cont:=1;
 i:=3;
 while i<=n do begin
  if a[i]=false then begin
   inc(cont);
   j:=i+i;
   while j<=n do begin
    a[j]:=true;
    j:=j+i;
   end;
  end;
  i:=i+2;
 end;

 assign(t,'ciur.out'); rewrite(t);
 writeln(t,cont);
 close(t);
end.