<for...to...do>
program phuongt;
uses crt;
var i: integer;
a: real;
begin
clrscr;
a:=0;
for i:=1 to 21 do if i mod 2 <> 0 then a:=a+1/i;
write('A = ', a);
readln
end.
<while...do>
program phuongt;
uses crt;
var i: integer;
a: real;
begin
clrscr;
a:=0; i:=1;
while i<=21 do
begin
if i mod 2 <> 0 then a:=a+1/i;
i:=i+1;
end;
write('A = ', a);
readln
end.