Program ciurul;
type numar = 0..2000000;
var fi,fo:text;
    d:array[2..2000000] of boolean;
    i,j,n,k:numar;
begin
     assign(fi,'ciur.in'); reset(fi); read(fi,n); close(fi); assign(fo,'ciur.out'); rewrite(fo); k:=0;
     for i:=2 to trunc(sqrt(n))+1 do if not(d[i]) then begin for j:=2 to n div i do d[i*j]:=true; k:=k+1; end;
     write(fo,k); close(fo);
end.