Write a function that returns a sequence (index begins with 1) of all the even characters from a string. If the string is smaller than two characters or longer than 100 characters, the function should return "invalid string". 
For example:
`````
"abcdefghijklm" --> ["b", "d", "f", "h", "j", "l"]
"a"             --> "invalid string"
`````
def even_chars(st): 
    return [ x for i, x in enumerate(st) if i%2 == 1] if 101 > len(st) > 1 else "invalid string" 
def even_chars(st): 
    return [ x for i, x in enumerate(st) if i%2 == 1] if 101 > len(st) > 1 else "invalid string" 