def sum_keep_digits(m: int, n: int, digit_count: int) -> int:
    """Finds the last base-10 digits of the sum of two non-negative integers.

    Args:
        m: The first non-negative integer addend.
        n: The second non-negative integer addend.
        digit_count: The number of least significant digits of the resulting
            sum that should be preserved.

    Returns:
        An integer consisting of the last ``digit_count`` digits (from most to
        least significant) of the sum ``m + n`` when written in base 10.
    """
    mod = 10**digit_count
    return ((m % mod) + (n % mod)) % mod