#include <stdio.h>  
#include <string.h>  
#define NMAX 1011  

int Case;  
int N, M, K, A[NMAX][NMAX], q[NMAX*NMAX][2], L[NMAX], cL[NMAX];
char S1[NMAX], S2[NMAX], Sir[NMAX], temp[NMAX], caux, saux;

int main()  
{  
     int i, j, nq, nt, l, c, k , ns, poz, start, x, y, sx, sy;

     freopen("seif.in", "r", stdin);  
     freopen("seif.out", "w", stdout);  
   
     scanf("%d", &Case);  
   
     while (Case--)  
     {
            memset(S1,'\0',sizeof(S1));
            memset(S2,'\0',sizeof(S2));
            scanf("%d", &K);  
            scanf(" ");
            gets(S1);
            scanf(" ");
            gets(S2);

            N = strlen(S1); M = strlen(S2);  
   
            for (i = 0; i < N; i++) temp[i] = S1[N-i-1];  
            for (i = 0; i < N; i++) S1[i] = temp[i];  
            for (i = 0; i < M; i++) temp[i] = S2[M-i-1];  
            for (i = 0; i < M; i++) S2[i] = temp[i];  
   
            memset(A,0,sizeof(A));
            memset(temp,'\0',sizeof(temp));
   
            for (i = 1; i <= N; i++)  
             for (j = 1; j <= M; j++)  
                 if (S1[i-1]==S2[j-1]) A[i][j] = A[i-1][j-1]+1;
                 else  
                 {  
                     A[i][j] = A[i][j-1];  
                     if (A[i][j]<A[i-1][j]) A[i][j] = A[i-1][j];  
                 }  
   
            nq = 0;  

            x = N; y = M;
            while(1)
            {
                  caux = '@';
                  for (i = x; i > 0; i--)
                     for (j = y; j > 0; j--)
                         if (S1[i-1]==S2[j-1]&&A[i][j]>=(K-nq))
                             if (caux<S1[i-1])
                                caux = S1[i-1], sx = i-1, sy = j-1;
                  if (caux=='@') break;
                  Sir[nq++] = caux;
                  x = sx; y = sy;
            }
   
            for (l = 0; l < nq; l++)
            {  
                 printf("%c", Sir[l]);
                 Sir[l] = '\0';  
            }  
            printf("\n");  
     }  
   
     return 0;  
       
}