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

int Case;  
int N, M, K, A[NMAX][NMAX], q[NMAX*NMAX][2], Lung[NMAX];
char S1[NMAX], S2[NMAX], Sir[NMAX], temp[NMAX], W[NMAX][NMAX];

int main()  
{  
     int i, j, nq, nt, l, c, k , nw = 0;

     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(W,'\0',sizeof(W));
            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;  

            for (i = 1; i <= N; i++)  
                 for (j = M; j > 0; j--)  
                     if (S1[i-1]==S2[j-1]&&A[i][j]>=K)
                         q[nq][0] = i, q[nq++][1] = j;
   
            for (j = 0; j < nq; j++)  
            {  
                 l = q[j][0]; c = q[j][1];  
                 nt = 0;  
                 k = A[l][c];  
                 while (k>0)  
                 {  
                     if (S1[l-1]==S2[c-1]) {  
                         k--; temp[nt++] = S1[l-1]; l--; c--;  
                        }  
                     else  
                         if ((A[l-1][c]>A[l][c-1])||((A[l-1][c]==A[l][c-1])&&(S1[l-2]>S2[c-2]))) l--;  
                         else c--;  
                 }
                 for (l = 0; l < nt; l++) W[nw][l] = temp[l], Lung[nw]++;
                 nw++;
            }

            for (i = 0; i < nw; i++)
                for (j = i+1; j < nw; j++)
                {
                        l = 0;
                        while (l < Lung[i]-1 && l < Lung[j]-1 && W[i][l]==W[j][l]) l++;
                        if ( (W[i][l]>W[j][l])||(W[i][l]==W[j][l]&&Lung[i]>Lung[j]) )
                        {
                           for (l = 0; l < Lung[i]; l++) temp[l] = W[i][l], W[i][l] = '\0';
                           nt = Lung[i];
                           for (l = 0; l < Lung[j]; l++) W[i][l] = W[j][l], W[j][l] = '\0';
                           Lung[i] = Lung[j];
                           for (l = 0; l < nt; l++) W[j][l] = temp[l], temp[l] = '\0';
                           Lung[j] = nt;
                        }
                }
   
            for (l = 0; l < Lung[nw-1]; l++)
            {  
                 printf("%c", W[nw-1][l]);
                 Sir[l] = '\0';  
            }  
            printf("\n");  
     }  
   
     return 0;  
       
}