s = gets.chomp
n, m = s.size, s.size / 2
pos = (0...m).find { s[_1] != s[~_1] }
if pos
	t = s[pos..~pos]
	if x = [t + t[0], t[-1] + t].find{ _1 == _1.reverse }
		s[pos..~pos] = x
		puts s
	else
		puts 'NA'
	end
else
	if n.even?
		puts s[...m] + 'a' + s[m..]
	else
		puts s[...m] + s[m] + s[m..]
	end
end