1st, 2nd, 3rd

1 - first
2 - second
3 - third
4 - fourth
5 - fifth
6 - sixth
7 - seventh
8 - eighth
9 -ninth
10 - tenth

1st
2nd
3rd
4th
5th
6th
7th
8th
9th
10th
11th - eleventh
12th - twelfth
13th
14th
15th
16th
17th
18th
19th
20th
21st
22nd
23rd
24th
...
30th
31st
32nd
33rd
34th
...

매우 간단한 규칙이지만 안 쓰면 잊어 먹어서 ...