#include<iostream>
#include<algorithm>
#include<cmath>
#include<cstdio>
using namespace std;
int n, l, r, p=-1, q=-1;
string s, ans;
int main()
{
    freopen ("code.in", "r", stdin);
    freopen ("code.out", "w" , stdout);
    cin>>n;
    cin>>s;
    l=0;
    r=n-1;
    //p=l;
    //q=r;
    for (int i=0; i<n; i++)
    {
        if (s[l]<s[r])
        {
            ans+=s[l];
            l++;
        }
        else
        if (s[l]>s[r])
        {
            ans+=s[r];
            r--;
        }
        else
        {
            p=l, q=r;
            while(s[p]==s[q] && p<q)
            {
                p++;
                q--;
            }
            if (p>=q)
            {
                ans+=s[l];
                l++;
            }
            else
            {
                if (s[p]<s[q])
                {
                   ans+=s[l];
                   l++;
                }
                else
                {
                   ans+=s[r];
                   r--;
                }
            }

        }
    }
    cout<<ans<<endl;
    return 0;
}