program cap_so_cong;
uses crt;
var a: array[1..100] of integer;
i, n, k: integer; {i la bien dem, k de luu cap so}
begin
clrscr;
write('N= '); readln(n);
for i:=1 to n do
begin
write('A(',i,')= '); readln(a[i]);
end;
{Bat dau phan kiem tra}
k:=a[2]-a[1];
i:=2;
repeat
i:= i+1;
until (a[i]<>a[i-1]+k) or (i>n);
if i>n then write('Day A la mot cap so cong')
else write('Day A khong phai la mot cap so cong');
readln
end.