Untitled

def is_safe_expression(expr: str) -> bool:
    allowed_chars = set('0123456789+-() ')
    for char in expr:
        if char not in allowed_chars:
            return False
    return True

def evaluate_expression(expr: str) -> int:
    if not is_safe_expression(expr):
        raise ValueError("Unsafe expression!")
    
    return int(eval(expr))

# Test cases
print(evaluate_expression('1+20'))  # 21
print(evaluate_expression('10-2+40'))  # 48
print(evaluate_expression('10- (1- 9)'))  # 18