
    In a transit system's sorted database of daily bus route IDs, where each route typically has both morning and evening service (appearing twice in the list), write a function to identify the single route ID that appears only once, indicating an unbalanced service schedule that requires attention. This route identification is crucial for maintaining balanced transit operations and ensuring all routes have corresponding return services.
    

    
def search(arr):
    """
    In a transit system's sorted database of daily bus route IDs, where each route typically has both morning and evening service (appearing twice in the list), write a function to identify the single route ID that appears only once, indicating an unbalanced service schedule that requires attention. This route identification is crucial for maintaining balanced transit operations and ensuring all routes have corresponding return services.
    

    """
def search(arr):
    """
    In a transit system's sorted database of daily bus route IDs, where each route typically has both morning and evening service (appearing twice in the list), write a function to identify the single route ID that appears only once, indicating an unbalanced service schedule that requires attention. This route identification is crucial for maintaining balanced transit operations and ensuring all routes have corresponding return services.
    

    """
    n = len(arr)
    XOR = 0
    for i in range(n):
        XOR = XOR ^ arr[i]
    return XOR