import java.util.Stack;

public class EvaluateExpression {

public int evaluateExpression(String s) {

Stack<Integer> stack = new Stack<>();

int currNum = 0;

int sign = 1;

int res = 0;

for (char c : s.toCharArray()) {

if (Character.isDigit(c)) {

currNum = currNum * 10 + c - '0';

}

// If the current character is an operator, add 'currNum' to

// the result after multiplying it by its sign.

else if (c == '+' || c == '-') {

res += currNum * sign;

// Update the sign and reset 'curr_num'.

sign = c == '-' ? -1 : 1;

currNum = 0;

}

// If the current character is an opening parenthesis, a new

// nested expression is starting.

else if (c == '(') {

// Save the current 'res' and 'sign' values by pushing them

// onto the stack, then reset their values to start

// calculating the new nested expression.

stack.push(res);

stack.push(sign);

res = 0;

sign = 1;

}

// If the current character is a closing parenthesis, a nested

// expression has ended.

else if (c == ')') {

// Finalize the result of the current nested expression.

res += sign * currNum;

// Apply the sign of the current nested expression's result

// before adding this result to the result of the outer

// expression.

res *= stack.pop();

res += stack.pop();

currNum = 0;

}

}

// Finalize the result of the overall expression.

return res + currNum * sign;

}

}