procedure main(args)
   n := integer(!args) | 5
   every !(A := list(n)) := list(n)
   A := zigzag(A)
   show(A)
end

procedure show(A)
    every writes(right(!A,5) | "\n")
end

procedure zigzag(A)
    x := [0,0]
    every i := 0 to (*A^2 -1) do {
        x := nextIndices(*A, x)
        A[x[1]][x[2]] := i
        }
    return A
end

procedure nextIndices(n, x)
    return if (x[1]+x[2])%2 = 0
           then if x[2] = n then [x[1]+1, x[2]] else [max(1, x[1]-1), x[2]+1]
           else if x[1] = n then [x[1], x[2]+1] else [x[1]+1, max(1, x[2]-1)]
end