def skjkasdkd(lst):
    def isPrime(n):
        for i in range(2,int(n**0.5)+1):
            if n%i==0:
                return False
        return True
    maxx = 0
    i = 0
    while i < len(lst):
        if(lst[i] > maxx and isPrime(lst[i])):
            maxx = lst[i]
        i+=1
    result = sum(int(digit) for digit in str(maxx))
    return result
def truncate_number(number: float) -> float:
    """ Given a positive floating point number, it can be decomposed into
    and integer part (largest integer smaller than given number) and decimals
    (leftover part always smaller than 1).
    Return the decimal part of the number.
    >>> truncate_number(3.5)
    0.5
    """
    return number % 1.0