#include <bits/stdc++.h> 
using namespace std;
int main()
{
    string s;
    int a[100], num = 0;
    int maxx = 0;
    int x = 0;
    cin >> s;
    for(int i = 0; i < s.length(); i++)
    {
        if(s[i] % 2 == 0)
        {
            a[x] == s[i];
            x++;
            num++;
        }
    }
    if(num != 0)
    {
        for(int i = 0; i < 101; i++)
        {
            if(a[i] > maxx)
            {
                maxx = a[i];
            }
        }
    }
    else
    {
        cout << "No";
        return 0;
    }
    cout << maxx;
    return 0;
}