def first_digits_of_sum(num_strs, n):
    """ Calculate the first `n` digits of the sum of a list of numbers. """
    cutoff = n + int((9 * len(num_strs))**0.1 + 1) - int(len(num_strs)**0.1)
    end_sum = 0
    for num_str in num_strs:
        end_sum += int(num_str[:cutoff])
    return int(str(end_sum)[:n])