n=int(input())
a=input().split()
a=list(map(int,a))
b=[]
for i in a:
    k=len(str(i))
    for j in range(k):
        m=int(str(i)[j:j+1])
        b.append(m)
b=sorted(b)
b.reverse()
s=0
for i in range(0,len(b)):
    s=s*10+b[i]
print(s)
/**************************************************************
	Problem: 1458
	User: admin
	Language: Python
	Result: Accepted
	Time:194 ms
	Memory:34480 kb
****************************************************************/