#!/bin/sh -

# Run time: O(number of lines)
# Memory: O(longest line)

# srand seed:
# "dd if=/dev/random 2>/dev/null | LC_ALL=C tr -d -c 1-9 | dd bs=1 count=19 2>/dev/null" | getline seed; srand(seed)
# + rand()

LC_ALL=C awk '
function urandom(n) {
	# return random [0, n)

	# maxn needs to be 2**(x*4), and cbs=x
	maxn = 4294967296

	if (n == 1)
		return 0

	if (n > maxn) {
		printf("n too large!\n") > "/dev/stderr"
		exit(5)
	}

	for (;;) {
		"dd if=/dev/random | LC_ALL=C tr -c -d 0-9a-f | dd conv=unblock cbs=8" | getline a

		r = ("0x" a) + 0
		quot = int(maxn / n) * n
		if (r >= quot)
			continue

		return r % n
	}
}

{
	#"jot -r 1 0 " (NR - 1) | getline a
	a = urandom(NR)
	#a = int(rand() * (NR))
	if (a == 0)
		save = $0
}
END { print save }'