def add_lists(L1, L2):
    '''(list, list) -> list
    Return a new list whose values are the corresponding
    values in L1 and L2 added together. Requirement: The 
    lists are the same length.
    >>> add_lists([1, 2, 3], [10, 20, 30])
    [11, 22, 33]
    >>> add_lists([2, 2, 2, 2], [4, 5, 6, 7])
    [6, 7, 8, 9]
    '''
    result = []
    for i in range(len(L1)):
        result.append(L1[i]+L2[i])
    return result


def palindrome(S):
    '''(str) -> bool
    Return True if the given string is a palindrome and 
    False otherwise.
    >>> palindrome('kayak')
    True
    >>> palindrome('racecar')
    True
    >>> palindrome('Racecar')
    False
    '''
    start = 0
    end = len(s) - 1
    while(start <= end):
        if (s[start] != s[end]):
            return False
        start = start + 1 
        end = end - 1
    return True

def count_hydrogen(molecule):
    '''(str) -> int
    Return the number of H atoms in the given molecule.
    >>> count_hydrogen('H20')
    2
    >>> count_hydrogen('NaOH')
    1
    >>> count_hydrogen('He')
    0
    >>> count_hydrogen('CH3OH')
    4
    '''
   

def grab_names(L):
    '''(list) -> list
    Return a list containing all the fields from L that are names 
    where a name is word that starts with a capital letter.
    >>> grab_names(['Anna', 35, 'lecturer', 'Toronto', 'Canada'])
    ['Anna', 'Toronto', 'Canada']
    >>> grab_names([25, True, 'windy', 'sunny'])
    []
    '''
    new_l = []
    
    for item in L:
        if type(item) == str:
            if item[0].isupper():
                new_l.append(item)
    return new_l

# Modifies list1 and list2
def interleave(list1, list2):
    '''(list, list) -> list
    Return a list that is the contents of list1 and list2 
    interleaved. If one list is longer, add the remainder of the 
    list to the end.
    >>> interleave([1, 4, 7], [2, 5])
    [1, 2, 4, 5, 7]
    >>> interleave([2,3], [])
    [2, 3]
    >>> interleave([], [3, 5, 7])
    [3, 5, 7]
    >>> interleave([1], [2, 3, 4, 5])
    [1, 2, 3, 4, 5]
    '''
    result = []
    while (len(list1) !=0 and len(list2) != 0):
        if list1[0] <= list2[0]:
            item = list1.pop(0)
        else:
            item = list2.pop(0)
        result.append(item)
            
    if len(list1) != 0:
        result = result + list1
    elif len(list2) != 0:
        result = result + list2
    return result