3993. Maximum Value of an Alternating Sequence

You are given three integers n, s, and m.

A sequence seq of integers of length n is considered valid if:

• seq[0] = s.
• The sequence is alternating, meaning that either:
  • seq[0] > seq[1] < seq[2] > ..., or
  • seq[0] < seq[1] > seq[2] < ....
• For every adjacent pair, |seq[i] - seq[i - 1]| <= m.

A sequence of length 1 is considered alternating.

Return the maximum possible element that can appear in any valid sequence.

Example 1:

Example 2:

Constraints:

• 1 <= n, s <= 109
• 1 <= m <= 105