var c:array[1..2000000] of integer;
    x,nr,i,k,n:longint;
    f:text;
begin
     assign(f,'ciur.in'); reset(f);
     readln(f,n);
     close(f);
     assign(f,'ciur.out'); rewrite(f);
     k:=3;                               nr:=0;
     while k<=trunc(sqrt(n)) do
     begin
          if c[k]=0 then begin
          x:=k+k;
          while x<=n do
          begin
               c[x]:=1;
               x:=x+k;
          end;           end;
          k:=k+2;
     end;  i:=1;
     while i<=n do
     begin
          i:=i+2;
          if c[i]=0 then inc(nr);
     end;
     writeln(f,nr);
     close(f);
end.