Problem:
Score : 300 points

Problem Statement

You are given a string s.
Among the different substrings of s, print the K-th lexicographically smallest one.

A substring of s is a string obtained by taking out a non-empty contiguous part in s.
For example, if s = ababc, a, bab and ababc are substrings of s, while ac, z and an empty string are not.
Also, we say that substrings are different when they are different as strings.

Let X = x_{1}x_{2}...x_{n} and Y = y_{1}y_{2}...y_{m} be two distinct strings. X is lexicographically larger than Y if and only if Y is a prefix of X or x_{j} > y_{j} where j is the smallest integer such that x_{j} \neq y_{j}.

Constraints

1 ≤ |s| ≤ 5000

s consists of lowercase English letters.

1 ≤ K ≤ 5

s has at least K different substrings.

Partial Score

200 points will be awarded as a partial score for passing the test set satisfying |s| ≤ 50.

Input

Input is given from Standard Input in the following format:

s
K

Output

Print the K-th lexicographically smallest substring of K.

Sample Input 1

aba
4

Sample Output 1

b

s has five substrings: a, b, ab, ba and aba.
Among them, we should print the fourth smallest one, b.
Note that we do not count a twice.

Sample Input 2

atcoderandatcodeer
5

Sample Output 2

andat

Sample Input 3

z
1

Sample Output 3

z

Solution in JavaScript (node.js v5.12) (judge verdict: Runtime Error)

process.stdin.resume();
process.stdin.setEncoding('utf8');
let count = 0;
let string, K;
process.stdin.on('data', function(data) {
    count++;
    // console.log(data);

    switch (count) {
        case 1:
            string = data.toString().toLowerCase();
            break;
        case 2:
            K =Number(data);
            break;
    }
});

process.stdin.on('end', function() {
    main(string, Number(data));
});

function main(string, K) {
    const substringCounts = string.length;

    if(substringCounts < 1 || 5000 < substringCounts)
        process.exit();

    if(K < 1 || 5 < K)
        process.exit();

    let stacks = [];
    let _substr = '';
    for(let i = 0; i <= substringCounts; i++) {
        for(let j = i; j <= substringCounts; j++) {
            _substr = string.substring(i, j);
            if(!stacks.includes(_substr) && !_substr.includes('\n') && _substr !== '')
                stacks.push(string.substring(i, j));
        }
    }
    stacks.sort();
    console.log(stacks[K-1]);
    process.exit();
};