Insert parentheses to minimize expression value

You are given a string expression of the form `A+B`, where `A` and `B` are non-empty strings of digits (no digit is `'0'`). You must insert exactly one pair of parentheses `(` and `)` into the expression such that: - The parentheses form a valid expression and **must include the plus sign**. - Any digits **outside** the parentheses remain adjacent to the parentheses and are interpreted as **multiplication** with the parenthesized sum. More precisely, choose a split of `A` into `A = L1 + L2` (concatenation) and a split of `B` into `B = R1 + R2` such that the resulting value is: - If `L1` is empty, treat it as multiplicative factor 1; otherwise factor is integer value of `L1`. - If `R2` is empty, treat it as multiplicative factor 1; otherwise factor is integer value of `R2`. Resulting value = `factor(L1) * (int(L2) + int(R1)) * factor(R2)`. Return the expression string with parentheses inserted that yields the **minimum** possible value. If multiple answers tie, return any one. Example: input `"435+122"` could become something like `"4(35+12)2"` (not necessarily optimal).