Làm giúp mình với ạ^^
Examples:
Input: 311
Output:313
Input:26622
Output:26262
Input:1213
Output:0

n=input()
a=[0]*10
k=''
for i in n:
    a[int(i)]+=1
s=0
x=True
for i in range(10):
    if a[i]%2!=0:
        s+=1
        j=i
        if s>1:
            x=False
            break
    elif a[i]==0:
        a[i]=-1
if x:
    if s==0:
        s=0
        for i in range(1,10):
            if s==1:
                k=k+'0'*(a[0]//2)
            if a[i]!=-1:
                s=+1
                k=k+str(i)*(a[i]//2)
        print(k+k[::-1])
    else:
        if a[0]==-1:
            for i in range(1,10):
                if a[i]!=-1:
                    k=k+str(i)*(a[i]//2)
            print(k+str(j)+k[::-1])
        elif a[0]%2==0:
            s=0
            a[j]-=1
            for i in range(1,10):
                if s==1:
                    k=k+'0'*(a[0]//2)
                if a[i]!=-1 and a[i]!=0:
                    s=+1
                    k=k+str(i)*(a[i]//2)
            if len(k+str(j)+k[::-1])==len(n):
                print(k+str(j)+k[::-1])
            else:
                print(0)
        else:
            s=0
            a[0]-=1
            for i in range(1,10):
                if s==1:
                    k=k+'0'*(a[0]//2)
                if a[i]!=-1:
                    s+=1
                    k=k+str(i)*(a[i]//2)
            print(k+str(0)+k[::-1])
else:
    print(0)