program a1;
var ch:char;
begin
writeln('введите текст');
repeat
readln(ch);
if ch='а' then ch:='б'
else if ch='б' then ch:='а';
if (ch='а')or(ch='б') then writeln(ch);
until ch='.';
end.
program a1;
var ch:char;
begin
writeln('введите текст');
repeat
readln(ch);
if ch='а' then ch:='б'
else if ch='б' then ch:='а';
if (ch='а')or(ch='б') then writeln(ch);
until ch='.';
end.