var i,n,nr:longint;
	a:array[1..2000000] of boolean;
    f:text;

procedure mark(i:longint);
var d:longint;
begin
d:=2;
while i*d<=n do begin
a[d*i]:=false;
inc(d);
end;
end;

begin
nr:=0;
assign(f,'ciur.in');
reset(f);
read(f,n);
close(f);
fillchar(a,sizeof(a),true);
a[1]:=false;

for i:=2 to n do
	if (a[i]) then begin
							  inc(nr);
							  mark(i);		
 							  end
	else a[i]:=false;
assign(f,'ciur.out');
rewrite(f);
write(f,nr);
close(f);
end.