A:=a+b;
b:=a-b;
a:=a-b;
var a,b:real;
procedure change(var a, b: real);
begin
a := a + b; writeln(a);
b := a - b; writeln(b);
a := a - b; writeln(a);
end;
begin
writeln('a, b:');
readln(a, b);
writeln('a=', a);
writeln('b=', b);
change(a, b);
writeln('a=', a);
writeln('b=', b);
readln;
end.