program numere_prime;
var i,nr,j,n:longint;
    cond:boolean;
    f,g:text;
begin
assign (f,'ciur.in'); reset (f);
assign (g,'ciur.out'); rewrite (g);
read (f,n);
i:=3;
nr:=1;
while (i<=n) do begin cond:=true;
                      for j:=2 to i div 2 do if (i mod j=0) then begin cond:=false;
                                                                       break;
                                                                 end;
                      if (cond=true) then nr:=nr+1;
                      i:=i+2;
                end;
write (g,nr);
close (f);
close (g);
end.