var i,n,j,p:longint;
    v:array[1..50] of longint;
    f,t:text;
begin
assign(f,'ciur.in');
assign(t,'ciur.out');
reset(f);
rewrite(t);
read(f,n);
for i:=1 to n do v[i]:=0;

for i:=2 to trunc(sqrt(n)) do
    begin
    for j:=2 to (n div i) do
    v[i*j]:=1;
    end;
p:=0;
for i:=2 to n do
if v[i]=0 then inc(p);
write(t,p);
close(f);
close(t);
end.