Скомпильте сами и убедитесь, что работает прога нормально
прога 1000

ЛИСТИНГ:
program ab;
var
a,b,c:longint;
fi,fo:text;
begin
assign(fi,'input.txt');
reset(fi);
read(fi,a);
read(fi,b);
c:=a+b;
close(fi);
assign(fo,'output.txt');
rewrite(fo);
write(fo,c);
close(fo);
end.

First of all, you must write in English, because it is an international site.

You cannot get Ac, because you must use standard input and output. Remove "Assign","Reset","Rewrite" and "Close".