#include <iostream>
#include<string>
#include<vector>
#include<algorithm>
#define pb push_back
using namespace std;
int main()
{
int x,y,t,n;
string s,w;
vector<string>v;
cin>>t;
while(t--)
{
w="";
cin>>s>>n;
for(x=0;x<s.length();x++)
{
for(y=s.length()-x;y>=1;y--)
{
w=s.substr(x,y);
v.pb(w);
}
}
sort(v.begin(),v.end());
w="";
for(x=0;x<v.size();x++)
{
w=w+v[x];
}
cout<<w[n-1]<<endl;
}
return 0;
}
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