var fin,fout:text;
    n:longint;
    a:array[1..2000000] of boolean;

procedure init(n:longint);
var i:longint;
begin
for i:=1 to n do a[i]:=true;
end;

procedure afis;
var i,k:longint;
begin
k:=0;
for i:=2 to n do
 if a[i] then inc(k);
write(fout,k);
end;

procedure prim;
var i,j:longint;
begin
for i:=2 to trunc(sqrt(n)) do
 if a[i] then
  begin
   j:=i;
   while j<=trunc(sqrt(n)) do
    begin
     j:=j+i;
     a[j]:=false;
    end;
  end;
end;

begin
assign(fin,'ciur.in');
reset(fin);
assign(fout,'ciur.out');
rewrite(fout);
read(fin,n);
init(n);
prim;
afis;
close(fin);
close(fout);
end.