func main()
	var s: []char :: cui@input()
	var n: int :: ^s
	var ans: int :: 0
	for i(0, n - 1)
		for j(i + 1, n)
			if(i = 0 & j = n)
				skip j
			end if
			var t: []char :: s.sub(i, j - i)
			var u: []char :: ##t
			do u.reverse()
			if(t = u)
				do ans :: [ans, ^t].max()
			end if
		end for
	end for
	do cui@print("\{ans}\n")
end func