one more method

from itertools import combinations

x=raw_input()
y=x.split()
N=int(y[0])
K=int(y[1])

z=raw_input()
Arr=z.split()
Main=[]
for i in Arr:
    Main.append(int(i))

combs=combinations(Main,K)
shortcombs=set(combs)


def FindXOR(L):
    ls=list(L)
    maxno=max(ls)
    if(maxno!=0):
        lent=len(str(maxno))
        ans=[0]*lent
        for i in L:
            k=lent-1
            var=i
            while(k>=0):
                ans[k]=ans[k]+var%10
                k=k-1
                var=var/10
                if(var==0):
                    break

        for i in range(0,len(ans)):
            ans[i]=ans[i]%10

        result="".join(map(str,ans))
        return int(result)
    else:
        return 0


maxnum=0
for i in shortcombs:
    ans=FindXOR(i)
    if(ans>maxnum):
        maxnum=ans
    if(ans==9):
        break

print(maxnum)