program capsocong;
uses crt;
var A:array[1..100]of integer;
    i,n:byte;
    k:integer;
begin
   clrscr;
   write('Ban muon nhap bao nhieu so? N= ');
   readln(n);
   for i:=1 to n do
   begin
      write('So thu ',i,': ');
      readln(a[i]);
   end;
   k:=a[2]-a[1];
   for i:=3 to n do
      if (a[i]-a[i-1]<>k) then
      begin
         write('Khong phai cap so cong!');
         readln;
         halt; {Thoat chuong trinh}
      end
      else
      begin
         if i=n then
         begin
            write('Day vua nhap la cap so cong');
            readln;
         end
      end;
end.