#include <iostream>
#include <cstring>
#define int long long
#define endl '\n'
#define QAQ ios::sync_with_stdio(false),cin.tie(0),cout.tie(0)
using namespace std;
signed main()
{
    QAQ;
    string s;
    cin>>s;
    
        for(int i=0;i<(s.size())/2;i++)
        {
            if(s[i]>s[s.size()-1-i])
                s[i]=s[s.size()-1-i];
            else
                s[s.size()-1-i]=s[i];
        }
        cout<<s;
    
    
    
    
    return 0;
}