1, 1 = 2
2, 2 = 4
2, 2, 2 = 6
3, 3 = 6
4, 4 = 8
5, 5 = 10
6, 6 = 12
7, 7 = 14
8, 8 = 16
19, 23 = 42
119, 123 = 242
# negative
-1, -1 = -2
-2, -1 = -3
# edge cases
0, 1 = 1
-0, 1 = 1
0, -1 = -1
-0, -1 = -1
1, 0 = 1
1, -0 = 1
2, 0 = 2
-1, 0 = -1
-1, -0 = -1
1, -1 = 0
2, -2 = 0
3, -3 = 0
4, -4 = 0
5, -5 = 0
6, -6 = 0
7, -7 = 0
8, -8 = 0
9, -9 = 0
10, -10 = 0
11, -11 = 0
12, -12 = 0
13, -13 = 0
14, -14 = 0
15, -15 = 0
16, -16 = 0
17, -17 = 0
18, -18 = 0
19, -19 = 0
20, -20 = 0
21, -21 = 0
22, -22 = 0
23, -23 = 0
$ cp tests/large_sum.txt tests/sum.txt
$ perl tests/t24.pl