def laceStrings(s1, s2):
    """
    s1 and s2 are strings.

    Returns a new str with elements of s1 and s2 interlaced,
    beginning with s1. If strings are not of same length, 
    then the extra elements should appear at the end.
    """
    # initialize the length of the shorter string
    length = min(len(s1), len(s2))
    
    # initialize the longer string
    longer_string = max(s1, s2, key = len)
    
    # initialize result string
    result = ''
    
    # for the length of the shorter string
    for i in range(length):
    
        # add element i from s1 to the result string
        result += s1[i]
        
        # add element i from s2 to the result string
        result += s2[i]
    
    # add any leftover chars from s1 or s2 to the result string
    result += longer_string[length: ]
    
    # return result string
    return result