Adding without using a + or - sign
R (24 characters)
length(sequence(scan()))

What this does:

scan reads input from STDIN (or a file)
sequence generates integer sequences starting from 1 and concatenates the sequences.  For example, sequence(c(2, 3)) results in the vector 1 2 1 2 3
length calculates the number of elements in the concatenated vector

Example 1:
&gt; length(sequence(scan()))
1: 123
2: 468
3:
Read 2 items
[1] 591

Example 2:
&gt; length(sequence(scan()))
1: 702
2: 720
3:
Read 2 items
[1] 1422