var f,g:text;
    s:array[1..2000000] of boolean;
    n,i,k,nr:longint;
begin
     assign(f,'ciur.in'); reset(f);
     assign(g,'ciur.out'); rewrite(g);
     readln(f,n);
     nr:=n-1;
     fillchar(s,sizeof(s),true);
     for i:=2 to trunc(sqrt(n)) do
     begin
          k:=i+i;
          while k<=n do
          begin
               if s[k]=true then dec(nr);
               s[k]:=false;
               k:=k+i;
          end;
     end;
     writeln(g,nr);
     close(g);
end.