#include <iostream>
#include <cmath>

using namespace std;

int cif(long a, int b);
int PalMinim(long n);
int Nrcifre(long n);

int main()
{
    int n;
    cin >> n;
    cout << PalMinim(n);
}

int cif(long a, int b)
{
    int cnt = 0;
    if(!a && !b) cnt = 1;
    while(a)
    {
        if(a % 10 == b) cnt++;
        a/=10;
    }
    return cnt;
}

int PalMinim(long n)
{

    int m = 0, nrap, i, c;
    if(Nrcifre(n) % 2 == 0)
    {
        for(c = 9; c >= 0; c--)
        {
            nrap = cif(n,c);
            if(nrap % 2 != 0)
                return 0;
            else
                for(i = 1; i<=nrap/2; i++)
                    m = m * 10 + c;
        }
    }
    else
    {
        int ok = - 1;
        for(c = 9; c >= 0, ok <= 0; c--)
        {
            nrap = cif(n,c);
            if(nrap % 2 == 1)
            {ok++;
                if(nrap == 1) m = m * 10 + c;
                else
                {
                    for(i = 1; i<=nrap/2; i++)
                    m = m * 10 + c;
                }
            }
            else
            {
                for(i = 1; i<=nrap/2; i++)
                    m = m * 10 + c;
            }
            return 0;
        }
    }
    n = m;
    while(m)
    {
        n = n * 10 + m % 10;
        m /= 10;
    }
    return n;
}

int Nrcifre(long n)
{
    int nr = 0;
    if(n == 0) nr = 1;
    while(n)
    {
        n++;
        n/=10;
    }
    return nr;
}