The R language: No calls to `+` or `-`...

    sum(as.numeric(readLines(stdin(), 2)))

Example:

    > sum(as.numeric(readLines(stdin(), 2)))
    123
    456
    [1] 579

The `[1] 579` is the answer 579 (the `[1]` is to keep track of where in the result vector your are since in R all values are vectors - in this case of length 1)

Note that R has `+` operators just like most languages - it just so happens that it has `sum` too that sums up a bunch of vectors...

    > sum(1:10, 101:110)
    [1] 1110