def evaluate_expression(s: str) -> int:

stack = []

curr_num, sign, res = 0, 1, 0

for c in s:

if c.isdigit():

curr_num = curr_num * 10 + int(c)

# If the current character is an operator, add 'curr_num' to

# the result after multiplying it by its sign.

elif c == '+' or c == '-':

res += curr_num * sign

# Update the sign and reset 'curr_num'.

sign = -1 if c == '-' else 1

curr_num = 0

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

# nested expression is starting.

elif 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.append(res)

stack.append(sign)

res, sign = 0, 1

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

# expression has ended.

elif c == ')':

# Finalize the result of the current nested expression.

res += sign * curr_num

# 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()

curr_num = 0

# Finalize the result of the overall expression.

return res + curr_num * sign