def get_least_ocurring_element(arr):
    unique_elems = set(arr[:])
    least_count = len(arr)
    for i in unique_elems:
        current_count = arr.count(i)
        if (current_count < least_count):
            least_count = current_count
            least_ocurring = i
    return least_ocurring

elements = input("Enter the elements with space as separator: ")
print(get_least_ocurring_element(elements.rsplit()))