` ````
```

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You are given a string `expression`

representing a Lisp-like expression to return the integer value of.

The syntax for these expressions is given as follows.

`(let v1 e1 v2 e2 ... vn en expr)`

, where `let`

is always the string `"let"`

, then there are 1 or more pairs of alternating variables and expressions, meaning that the first variable `v1`

is assigned the value of the expression `e1`

, the second variable `v2`

is assigned the value of the expression `e2`

, and so on `expr`

.

`(add e1 e2)`

where `add`

is always the string `"add"`

, there are always two expressions `e1, e2`

, and this expression evaluates to the addition of the evaluation of `e1`

and the evaluation of `e2`

.

`(mult e1 e2)`

where `mult`

is always the string `"mult"`

, there are always two expressions `e1, e2`

, and this expression evaluates to the multiplication of the evaluation of `e1`

and the evaluation of `e2`

.

**Evaluation Examples:**

Input:(add 1 2)Output:3Input:(mult 3 (add 2 3))Output:15Input:(let x 2 (mult x 5))Output:10Input:(let x 2 (mult x (let x 3 y 4 (add x y))))Output:14Explanation:In the expression (add x y), when checking for the value of the variable x, we check from the innermost scope to the outermost in the context of the variable we are trying to evaluate. Since x = 3 is found first, the value of x is 3.Input:(let x 3 x 2 x)Output:2Explanation:Assignment in let statements is processed sequentially.Input:(let x 1 y 2 x (add x y) (add x y))Output:5Explanation:The first (add x y) evaluates as 3, and is assigned to x. The second (add x y) evaluates as 3+2 = 5.Input:(let x 2 (add (let x 3 (let x 4 x)) x))Output:6Explanation:Even though (let x 4 x) has a deeper scope, it is outside the context of the final x in the add-expression. That final x will equal 2.Input:(let a1 3 b2 (add a1 1) b2)Output4Explanation:Variable names can contain digits after the first character.

**Note:**

`expression`

is well formatted: There are no leading or trailing spaces, there is only a single space separating different components of the string, and no space between adjacent parentheses. The expression is guaranteed to be legal and evaluate to an integer.`expression`

is at most 2000. (It is also non-empty, as that would not be a legal expression.)
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