uses crt;
var a:array[1..100] of integer;
n,i,d,s,dd:integer;
begin
clrscr;
repeat
write('nhap n: '); readln(n);
until n>1;
for i:=1 to n do
begin
write ('nhap phan tu thu ',i,': ');  readln(a[i]);
if a[i]>0 then inc(dd);
end;
writeln ('trong day co ',dd,' so duong');
d:=1;
s:=abs(a[2]-a[1]);
for i:=3 to n do if abs(a[i]-a[i-1])=s then d:=d+1 else break;
if d=n-1 then write('day la day so cap so cong')
else write('day khong phai la day so cap so cong');
readln;
end.

program bai10;

Uses crt;

Var

        n,i,dem,sc:integer;

        A:array[1..100] of integer;

Begin

          clrscr;

        repeat

           write('Nhap so phan tu: '); readln(n);

        Until n>=2;

           for i:=1 to n do readln(A[i]);

           Dem:=1; sc:=abs(A[2]-A[1]);

           For i:=3 to n do if abs(A[i]-A[i-1])=sc then dem:=dem+1 else break;

          If dem=n-1 then write('Yes') else write('No');

        readln;

End.

#Bạn kiểm tra lại nha, có sai sót mong bạn thông cảm

#Chuc_ban_hoc_tot