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 C (GCC 5.4.1) (judge verdict: Runtime Error)

#include<stdio.h>
#include<string.h>

int main(){
		int n=0,k,i,j,l,m=0,c=0;
		char s[5001],subs[50*50][51]={0};
		scanf("%s%d",s,&k);
		while(s[n]!=0)n++;
		//printf("%d\n",n);
		for(i=0;i<n;i++){
				for(j=i;j<n;j++){
						for(l=i;l<=j;l++){
								subs[c][l-i]=s[l];
						}
						//printf("%s\n",subs[c]);
						c++;
				}
		}
		for(i=0;i<c;i++){
				for(j=0;j<c;j++){
						if(strcmp(subs[i],subs[j])<0){
								char tmp[51]={0};
								strcpy(tmp,subs[i]);
								for(l=0;subs[i][l]!=0;l++)subs[i][l]=0;
								strcpy(subs[i],subs[j]);
								for(l=0;subs[j][l]!=0;l++)subs[j][l]=0;
								strcpy(subs[j],tmp);
						}
				}
		}
		for(i=1;i<c;i++){
				//printf("%s\n",subs[i]);
				if(strcmp(subs[i-1],"")!=0&&strcmp(subs[i-1],subs[i])!=0)m++;
				if(m>k)break;
		}
		printf("%s\n",subs[m]);
		return 0;
}