0 + 0 = 00 + 0 = 0
3 + 0 = 33 + 0 = 3
99 + 0 = 9999 + 0 = 99
0 + 1 = 10 + 1 = 1
1 + 1 = 21 + 1 = 2
2 + 1 = 32 + 1 = 3
3 + 1 = 43 + 1 = 4
4 + 1 = 54 + 1 = 5
4 + 1 = 1 + 44 + 1 = 1 + 4