
    In a sorted list of delivery vehicle IDs where each vehicle is recorded twice during its route (at departure and return), write a function to identify the single vehicle ID that appears only once, representing the vehicle that hasn't yet returned to the depot. The vehicle IDs are automatically logged in ascending order, and all vehicles except one have completed their routes.
    

    
def search(arr):
    """
    In a sorted list of delivery vehicle IDs where each vehicle is recorded twice during its route (at departure and return), write a function to identify the single vehicle ID that appears only once, representing the vehicle that hasn't yet returned to the depot. The vehicle IDs are automatically logged in ascending order, and all vehicles except one have completed their routes.
    

    """
def search(arr):
    """
    In a sorted list of delivery vehicle IDs where each vehicle is recorded twice during its route (at departure and return), write a function to identify the single vehicle ID that appears only once, representing the vehicle that hasn't yet returned to the depot. The vehicle IDs are automatically logged in ascending order, and all vehicles except one have completed their routes.
    

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