program pht;
uses crt;
var A: array[1..500] of real;
i, n: integer;
s: real;
op: text;
begin
clrscr;
assign(op, 'D:\ketqua.txt');
rewrite(op);
write('Nhap n = '); readln(n);
s:=0;
for i:=1 to n do
begin
write('A[', i, '] ='); readln(A[i]);
if i mod 2 <> 0 then s:=s+A[i] else s:=s-A[i];
end;
write(op, 'Tong = ', s);
close(op);
write('Mo file de xem ket qua');
readln
end.