type Tab=array[1..2000000] of boolean;
var f,g:text; a:tab; n,i,j,k:longint;

begin
assign(f, 'ciur.in');
reset(f);
assign(g, 'ciur.out');
rewrite(g);
k:=0;
readln(f, n);
for i:=1 to n do a[i]:=true;
for i:=2 to n do
if a[i] then begin
                j:=i;
                inc(k);
                while j+i<=n do
                begin
                j:=j+i;
                a[j]:=false;
                end;
                end;
write(g, k);
close(f); close(g);
end.