Given a string s representing a valid mathematical expression, implement a basic calculator to evaluate it, and return the result.

Note: You are not allowed to use any built-in function which evaluates strings as mathematical expressions, such as eval().

Examples

Example 1

Input:  s = "1 + 1"
Output: 2

Example 2

Input:  s = " 2-1 + 2 "
Output: 3

Example 3

Input:  s = "(1+(4+5+2)-3)+(6+8)"
Output: 23

Constraints

• 1 <= s.length <= 3 * 10⁵
• s consists of digits, '+', '-', '(', ')', and ' '
• s represents a valid expression
• '+' is not used as a unary operation (i.e., "+1" and "+(2 + 3)" are invalid)
• '-' could be used as a unary operation (i.e., "-1" and "-(2 + 3)" are valid)
• There will be no two consecutive operators in the input