у 10: 9 и 11
у 20: 19 и 21
у 30: 29 и 31
у 40: 39 и 41
у 50: 49 и 51
у 60: 59 и 61
у 70: 69 и 71
у 80: 79 и 81
9,10,11.
19,20,21.
29,30,31.
39,40,41.
49,50,51.
59,60,61.
69,70,71.
79,80,81.
89,90,91.
