var a:array[1..2000000] of byte;
    i,j,n,nr:integer;
    f,g:text;
begin
assign(f,'ciur.in');reset(f);
assign(g,'ciur.out');rewrite(g);
readln(f,n);close(f);
nr:=0;
for i:=2 to (trunc(sqrt(n))+1) do
 if a[i]=0 then begin
                 j:=2*i;
                 a[j]:=1;
                 while j<=n do begin
                                j:=j+i;
                                a[j]:=1;
                               end;
                end;
for i:=2 to n do if a[i]=0 then inc(nr);
write(g,nr);close(g);


end.