Iroha has a sequence of N strings S_1, S_2, ..., S_N. The length of each string is L.

She will concatenate all of the strings in some order, to produce a long string.

Among all strings that she can produce in this way, find the lexicographically smallest one.

Here, a string s=s_1s_2s_3...s_n is lexicographically smaller than another string t=t_1t_2t_3...t_m if and only if one of the following holds:

* There exists an index i(1≦i≦min(n,m)), such that s_j = t_j for all indices j(1≦j<i), and s_i<t_i.
* s_i = t_i for all integers i(1≦i≦min(n,m)), and n<m.

Constraints

* 1 ≦ N, L ≦ 100
* For each i, the length of S_i equals L.
* For each i, S_i consists of lowercase letters.

Input

The input is given from Standard Input in the following format:


N L
S_1
S_2
:
S_N


Output

Print the lexicographically smallest string that Iroha can produce.

Example

Input

3 3
dxx
axx
cxx


Output

axxcxxdxx
N,L=map(int,raw_input().split())
S=[]
for i in range(N):
    S.append(raw_input())
#print S
S_num=[]
for i in range(N):
    s_num=""
    for alpha in S[i]:
        s_num+="{:0=2}".format(ord(alpha)-ord("a")+1)
    S_num.append([int(s_num),i])

S_num.sort()
S_sort=[str(s_num[0]) if len(str(s_num[0]))%2==0 else "0"+str(s_num[0]) for s_num in S_num]
S_num_sort="".join(S_sort)
#print S_num_sort

S_num_2=[S_num_sort[i*2:i*2+2] for i in xrange(len(S_num_sort)/2)]
#print S_num_2
S_alpha=[chr(96+int(s_num_2)) for s_num_2 in S_num_2]
Ans="".join(S_alpha)

print Ans