Program p1;
var k,n,i : longint;
    f,g : text;

Function prim(k : longint) : boolean;
var j : longint;
    t : boolean;
begin
j:=2;
t:=true;
while (t) and (j*j<=k) do
begin
if k mod j=0 then t:=false;
inc(j);
end;
end;

begin
assign(f,'ciur.in');
reset(f);
readln(f,n);
close(f);
k:=0;
for i:=1 to n do
if prim(i) then inc(k);
assign(g,'ciur.out');
rewrite(g);
writeln(g,k);
close(g);
end.