Problem:
Score : 100 points

Problem Statement

You are given strings s and t.
Find one longest string that is a subsequence of both s and t.

Notes

A subsequence of a string x is the string obtained by removing zero or more characters from x and concatenating the remaining characters without changing the order.

Constraints

s and t are strings consisting of lowercase English letters.

1 \leq |s|, |t| \leq 3000

Input

Input is given from Standard Input in the following format:

s
t

Output

Print one longest string that is a subsequence of both s and t.
If there are multiple such strings, any of them will be accepted.

Sample Input 1

axyb
abyxb

Sample Output 1

axb

The answer is axb or ayb; either will be accepted.

Sample Input 2

aa
xayaz

Sample Output 2

aa

Sample Input 3

a
z

Sample Output 3

The answer is (an empty string).

Sample Input 4

abracadabra
avadakedavra

Sample Output 4

aaadara

Solution in OCaml (4.02.3) (judge verdict: Time Limit Exceeded)

let rec find c s =
    match s with
    | [] -> None
    | sc :: s' ->
        if sc = c
        then Some(s')
        else find c s'

let longer s1 s2 =
    if String.length s1 >= String.length s2
    then s1
    else s2

let rec solve s t =
    match s with
    | [] -> ""
    | sc :: s' ->
        match find sc t with
        | None -> solve s' t
        | Some(t') -> longer (solve s' t) (sc ^ solve s' t')

let () =
    let s =
        read_line () |> Str.split (Str.regexp "")
    in
    let t =
        read_line () |> Str.split (Str.regexp "")
    in
    print_endline @@ solve s t